For what it's worth VAT isn't uniform across the EU either. IIRC the EU specifies minimums, but countries are allowed higher rates and can manage their own exclusions too.

It can get even more complicated here because you can have a county and/or city sales tax add-on so sales tax can vary from city to city.. Doesn't matter to much until you get into big purchases like cars that people starting buying cars in the lowest tax cities. So then the state starting requiring that the tax to be calculated to the address where you are registered.