Earlier quoted context omitted.
So, implement sales tax like Europe does VAT and include it in on the shelf price, and make sure all shelf prices end in 0 or 5. Then, adding up items in a cart will also end in 0 or 5, and the tax is already included, so there is no math beyond the addition that could change the total to anything ending in something that is not 0 or 5. No matter how people pay, cash or card, the price will be the same, and it will a…
America is allergic to baked in taxes - you've got to keep the appearance of a deal even when there isn't one. America also embraces a lot of junk and hidden fees - ticketmaster is a great example of this. I think consumers would love having baked in taxes and clear prices and were the government functional I'd hope that a consumer advocacy agency could enforce this - but that's simply not where we are right now.
By comparison, in Japan the consumption tax is 10% for most items (8% for groceries and takeout), and it's the same nationwide.
In addition, there are sometimes fees that are prohibited by law from being baked in. For example, California has a statewide ban on free "single-use" bags in grocery stores and some other businesses. These businesses are required to charge their customers for bags, and they are not allowed to bake it into the price. Some municipalities have extended this to disposable cups as part of an effort to discourage them in favor of reusable cups. For example, Santa Cruz mandates a 25 cent fee on disposable cups. The Costco $1.50 hot dog + drink combo is normally $1.50 + sales tax, but in Santa Cruz it's $1.50 + $.25 mandatory cup fee + sales tax (yes, the cup is taxable). I have yet to see someone bring a disposable cup to Costco or to other places where paper cups are sold, however.
Having baked-in taxes will require big changes about how taxes and fees work in America, the land of extra sales taxes, extra fees, surcharges, and tipping.