Taxes, discounts, and fees may be created in a Catalog to apply at the order level, or within a specific Category to apply at the item level.
Can I access reduced interchange rates if I don’t charge tax?
Visa and Mastercard have very particular rules about what is required in order to receive level 2/3 rates. The one requirement that typically causes the most frustration for merchants is a Tax Value. Per Visa/Mastercard’s rules, you are required to submit a tax value with your sale if you want to qualify for the lowest rates.