diff --git a/src/pretix/base/services/cart.py b/src/pretix/base/services/cart.py
index c9ddf51a9a..66eaa0b1fc 100644
--- a/src/pretix/base/services/cart.py
+++ b/src/pretix/base/services/cart.py
@@ -53,6 +53,7 @@ from django.utils.translation import (
 )
 from django_scopes import scopes_disabled
 
+from pretix.base.decimal import round_decimal
 from pretix.base.i18n import language
 from pretix.base.media import MEDIA_TYPES
 from pretix.base.models import (
@@ -916,6 +917,8 @@ class CartManager:
                 if custom_price > 99_999_999_999:
                     raise CartError(error_messages['price_too_high'])
 
+                custom_price = round_decimal(custom_price, currency=self.event.currency)
+
             op = self.AddOperation(
                 count=i['count'],
                 item=item,
@@ -1038,6 +1041,8 @@ class CartManager:
                 if custom_price > 99_999_999_999:
                     raise CartError(error_messages['price_too_high'])
 
+                custom_price = round_decimal(custom_price, currency=self.event.currency)
+
             # Fix positions with wrong price (TODO: happens out-of-cartmanager-transaction and therefore a little hacky)
             for ca in current_addons[cp][a['item'], a['variation']]:
                 if ca.listed_price != listed_price:
diff --git a/src/tests/presale/test_cart.py b/src/tests/presale/test_cart.py
index ab0a852fcd..72eb9661f3 100644
--- a/src/tests/presale/test_cart.py
+++ b/src/tests/presale/test_cart.py
@@ -697,6 +697,42 @@ class CartTest(CartTestMixin, TestCase):
         self.assertIsNone(objs[0].variation)
         self.assertEqual(objs[0].price, 23)
 
+    def test_free_price_rounding(self):
+        self.ticket.free_price = True
+        self.ticket.save()
+
+        response = self.client.post('/%s/%s/cart/add' % (self.orga.slug, self.event.slug), {
+            'item_%d' % self.ticket.id: '1',
+            'price_%d' % self.ticket.id: '40.1234',
+        }, follow=True)
+        self.assertRedirects(response, '/%s/%s/?require_cookie=true' % (self.orga.slug, self.event.slug),
+                             target_status_code=200)
+
+        with scopes_disabled():
+            cr1 = CartPosition.objects.get()
+            assert cr1.listed_price == Decimal('23.00')
+            assert cr1.custom_price_input == Decimal('40.12')
+            assert cr1.price == Decimal('40.12')
+
+    def test_free_price_rounding_jpy(self):
+        self.event.currency = "JPY"
+        self.event.save()
+        self.ticket.free_price = True
+        self.ticket.save()
+
+        response = self.client.post('/%s/%s/cart/add' % (self.orga.slug, self.event.slug), {
+            'item_%d' % self.ticket.id: '1',
+            'price_%d' % self.ticket.id: '40.1234',
+        }, follow=True)
+        self.assertRedirects(response, '/%s/%s/?require_cookie=true' % (self.orga.slug, self.event.slug),
+                             target_status_code=200)
+
+        with scopes_disabled():
+            cr1 = CartPosition.objects.get()
+            assert cr1.listed_price == Decimal('23.00')
+            assert cr1.custom_price_input == Decimal('40.00')
+            assert cr1.price == Decimal('40.00')
+
     def test_variation_inactive(self):
         self.shirt_red.active = False
         self.shirt_red.save()
@@ -3060,6 +3096,31 @@ class CartAddonTest(CartTestMixin, TestCase):
         assert cp1.addons.count() == 3
         assert all(a.price == Decimal('12.00') for a in cp1.addons.all())
 
+    @classscope(attr='orga')
+    def test_free_price_rounding(self):
+        self.event.settings.locales = ['de']
+        self.event.settings.locale = 'de'
+        self.event.currency = "JPY"
+        self.event.save()
+
+        self.workshop1.free_price = True
+        self.workshop1.save()
+        cp1 = CartPosition.objects.create(
+            event=self.event, cart_id=self.session_key, item=self.ticket,
+            price=23, expires=now() - timedelta(minutes=10)
+        )
+
+        response = self.client.post('/%s/%s/checkout/addons/' % (self.orga.slug, self.event.slug), {
+            'cp_{}_item_{}'.format(cp1.pk, self.workshop1.pk): '1',
+            'cp_{}_item_{}_price'.format(cp1.pk, self.workshop1.pk): '99,99',
+        }, follow=True)
+        self.assertRedirects(response, '/%s/%s/checkout/questions/' % (self.orga.slug, self.event.slug),
+                             target_status_code=200)
+        with scopes_disabled():
+            assert cp1.addons.count() == 1
+            assert cp1.addons.first().item == self.workshop1
+            assert cp1.addons.first().price == Decimal('100')
+
     @classscope(attr='orga')
     def test_change_number(self):
         cp1 = CartPosition.objects.create(