Huh? How does the buyer know what is needed when it's easier for the seller to know and add it to every POS exchange?
Actually the consumer, rightly named, is recipient of most services and provider of most labor. It should be the consumer who makes the tax determination rather than some elected, primarily government, administrative group which is playing this need against that want for staying in power purposes.
Just as the seller and employer determines a price which permits her to make profit or have services in competition so should the buyer and employee determine what are her needs form society and labor to survive in competition with others. We are talking about willing participants here aren't we?
I've always felt the mediator, government, is very lax in constraining either wage or tax attrition screwing the consumer on both ends. Placing the authority for taxing should be from individuals who should pay no taxes. rather consumers should determine how much of gross product is spent for necessary services and guide the government in taking it in the marketplace.