“Are you taxed before or after coupons are taken into account?”
You are responsible for sales tax before the coupon discounts, even when you get the item for free. If your total is $10.00 before coupons and you have $8.00 in coupon savings, you’re usually responsible for any applicable tax on the $10.00 subtotal. The exception is if your state does not charge sales tax on either food or non-food items. It also depends upon the store(s) you frequent.