Taxes are configured at the POS level and are not a function configured in Punchh nor do any redeemables, or discounts from Punchh have a tax configuration. If you are notice an item discounted from a Punchh discount is still charging tax, please check the specific menu item's Tax configuration/class in your POS.
If there are items that this is not occurring with, compare the set-ups of the two items.