Add rounding strategy to tax settings (#1039)

<!-- Ticket number or summary of work -->
# [TAX-2467]

## What changed?
* New **rounding strategy** field on tax settings.

## Release notes draft
* New rounding strategy field is now available on tax settings. This
affects basic tax provider outcomes (not automatic tax provider
outcomes).

⚠️ Will await the corresponding changes to be actioned before updating
our documentation.

[TAX-2467]:
https://bigcommercecloud.atlassian.net/browse/TAX-2467?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: theromulans

reference/tax_settings.v3.yml

@@ -170,6 +170,13 @@ components:
           enum:
             - ON_PAYMENT_CAPTURE
             - ON_ORDER_CREATION
+        rounding_strategy:
+          default: RATE_ROUNDING
+          type: string
+          description: This setting affects the rounding behaviour of tax amounts calculated by the basic tax provider. The NO_ROUNDING option offers a high accuracy total tax amount for orders. The RATE_ROUNDING option means every resulting tax rate amount has been rounded based on the active currency's precision settings. Note that tax is always calculated on the line item amount after discounts.
+          enum:
+            - NO_ROUNDING
+            - RATE_ROUNDING
     MetaOpen:
       title: Response meta
       type: object