That's not a problem anywhere else - if you have two (or two hundred) locations with different tax rates, just calculate whatever is the highest total, and adve

That's not a problem anywhere else - if you have two (or two hundred) locations with different tax rates, just calculate whatever is the highest total, and advertise that - you're definitely allowed to sell stuff for cheaper than you advertised, so if one location has a 2% lower tax rate, you can sell it cheaper there; or you can charge different pre-tax prices so that the total is the same, if that's more profitable for you; I've seen both options used when advertising prices in EU-wide international campaigns despite different VAT rates across EU countries.