My proposal is simple, Price tags should have all taxes applied to the final price.
When shopping, for cars or for groceries, you must either be decent at math, or carry a calculator to arrive at your final price due to state or federal sales tax, I propose that the +10% calculation should only be done once, at the burden of the seller, rather than potentially many many times as multiple customers buy the same priced gallon of milk or gasoline.
I believe this is more efficient for everyone involved, and a very obvious decision, that leads to less surprises at the register, and more honest price stickers from restaurant menus to clothing outlets.
Simple, non-controversial, and easy to implement given time.