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_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,