How should GNU Taler handle taxes?

Case Studies
1

A good question was raised in person about taxes handling in GNU Taler so let me put it here.

For now, the Taler Merchant Backend doesn’t embed an internal logic for managing taxes because of the complexity of the topic and considering that this question is already handled by ERPs and e-Commerce platforms.

Now, how should the Merchant Backend handle this?

cc @fdold @oec @how

2

I would expect the backend to be able to accept a known series of taxes (e.g., per-country and per-product-category VAT percentages). They should be stored, like I believe they are currently, as absolute value in a JSON field.

The Merchant backend UI should indeed make visible the taxes from a legal perspective)

Now, my use-case has a