Avalara tax plugin. Inconsistent tax rates of order total and order items

[RomanovM]

nopCommerce version: 4.60

Different methods are invoked to get tax rates for order total and order items, which in complex tax providers (e.g. Avalara tax plugin) can lead to their inconsistency and incorrect tax amounts.

See also support ticket 17116 for details (details below):

We have issues with orders whose billing address in a state that Teklynx doesn't have a nexus with:

• For states that literally has a 0% sales tax rate (Alaska, Delaware, Montana, New Hampshire and Oregon), it works well.
• For states we do charge tax in (Wisconsin, Arizona, North Carolina, Ohio), it works well too, taxes are well calculated and displayed.
• But for states without nexus (Florida, Hawaii, Minnesota, Missouri, Illinois), the standard tax rate is not null but as Teklynx doesn't have nexus final tax is 0%, we have issues: The total amount of order is correct (Avalara returns 0%) but the prices of order items are not correct as they included taxes (see attached screenshot of a sample on admin panel). In addition of an incorrect display on the orders report, this generates an error on payment plugin (stripe in our case): display to customer of order details is incorrect and depending on prices, it generates an error because of inconsistent values.

Note: We have the option "Use tax rate tables to estimate" validated. Without this option validated, the issues disappear but removing this option makes the number of pings to Avalara increasing too much and which results in a significant additional cost for our company.