A sales tax is not regressive, it's flat. Simply because it's not progressive doesn't make it the opposite.
The benefit is that you take the burden off the individual and leave it all to computers. There's a "Taxable" flag and the equation is simple. IF (item.category == Food or price < (select minprice from categorylimits where categorylimits.category = item.category)) then tax = 0 else tax = 0.25 * item.price
Done. What a beautiful world that would be.