Allow to round taxes on order-level (#5019)

* Allow to round taxes on order-level

* Rename get_cart_total

* Persist rounding mode with order

* Add general docs

* Order creation API

* Update fee algorithm

* Rounding on payment method change

* Round when splitting order

* Fix failing tests

* Add settings page

* Add tests

* Replace algorithm

* Add test case for currency rounding

* Improve order change

* Update flowchart

* Update discount logic (more hypothetical, we don't store rounding on cart positions atm)

* Rename internal method

* Fix typo

* Update help text

* Apply suggestions from code review

Co-authored-by: luelista <weller@rami.io>

* Order rounding refactor (#5571)

* Add RoundingCorrectionMixin providing before-rounding-values as properties

* Use gross_price_before_rounding in more places

* Update doc/development/algorithms/pricing.rst

Co-authored-by: Martin Gross <gross@rami.io>

* Allow to override on perform_order

* Rebase migration

* Fix event cancellation

---------

Co-authored-by: luelista <weller@rami.io>
Co-authored-by: Martin Gross <gross@rami.io>

src/tests/api/test_order_create.py

@@ -420,6 +420,7 @@ def test_order_create_simulate(token_client, organizer, event, item, quota, ques
             }
         ],
         'total': '21.75',
+        'tax_rounding_mode': 'line',
         'comment': '',
         'api_meta': {},
         "custom_followup_at": None,
@@ -3259,3 +3260,79 @@ def test_order_create_auto_pricing_explicit_discount_not_allowed(token_client, o
             }
         ]
     }
+
+
+@pytest.mark.django_db
+def test_order_create_rounding_mode(token_client, organizer, event, item, quota, question, taxrule):
+    res = copy.deepcopy(ORDER_CREATE_PAYLOAD)
+    res["tax_rounding_mode"] = "sum_by_net"
+    res['fees'][0]['_split_taxes_like_products'] = True
+    res['fees'][0]['value'] = Decimal("100.00")
+    res['positions'] = [
+        {
+            "item": item.pk,
+            "price": "100.00",
+        }
+    ] * 4
+
+    for simulate in (True, False):
+        res["simulate"] = simulate
+        resp = token_client.post(
+            '/api/v1/organizers/{}/events/{}/orders/'.format(
+                organizer.slug, event.slug
+            ), format='json', data=res
+        )
+        assert resp.status_code == 201
+        assert resp.data["total"] == "499.98"
+        assert resp.data["positions"][0]["price"] == "99.99"
+        assert resp.data["positions"][-1]["price"] == "100.00"
+
+    res["tax_rounding_mode"] = "sum_by_net_keep_gross"
+    for simulate in (True, False):
+        res["simulate"] = simulate
+        resp = token_client.post(
+            '/api/v1/organizers/{}/events/{}/orders/'.format(
+                organizer.slug, event.slug
+            ), format='json', data=res
+        )
+        assert resp.status_code == 201
+        assert resp.data["total"] == "500.00"
+        assert resp.data["positions"][0]["tax_value"] == "15.96"
+        assert resp.data["positions"][-1]["tax_value"] == "15.97"
+
+
+@pytest.mark.django_db
+def test_order_create_rounding_default_pretixpos_fallback(device, device_client, organizer, event, item, quota, question, taxrule):
+    res = copy.deepcopy(ORDER_CREATE_PAYLOAD)
+    res['fees'][0]['_split_taxes_like_products'] = True
+    res['fees'][0]['value'] = Decimal("100.00")
+    res['positions'] = [
+        {
+            "item": item.pk,
+            "price": "100.00",
+        }
+    ] * 4
+
+    event.settings.tax_rounding = "sum_by_net"
+
+    resp = device_client.post(
+        '/api/v1/organizers/{}/events/{}/orders/'.format(
+            organizer.slug, event.slug
+        ), format='json', data=res
+    )
+    assert resp.status_code == 201
+    assert resp.data["total"] == "499.98"
+    assert resp.data["positions"][0]["price"] == "99.99"
+    assert resp.data["positions"][-1]["price"] == "100.00"
+
+    device.software_brand = "pretixPOS Android"
+    device.save()
+    resp = device_client.post(
+        '/api/v1/organizers/{}/events/{}/orders/'.format(
+            organizer.slug, event.slug
+        ), format='json', data=res
+    )
+    assert resp.status_code == 201
+    assert resp.data["total"] == "500.00"
+    assert resp.data["positions"][0]["price"] == "100.00"
+    assert resp.data["positions"][-1]["price"] == "100.00"

src/tests/api/test_orders.py

@@ -306,6 +306,7 @@ TEST_ORDER_RES = {
     "url": "http://example.com/dummy/dummy/order/FOO/k24fiuwvu8kxz3y1/",
     "payment_provider": "banktransfer",
     "total": "23.00",
+    "tax_rounding_mode": "line",
     "comment": "",
     "api_meta": {},
     "custom_followup_at": None,