I think this is pretty easy. In reality there are stores that opened their hearts to bitcoin and have their own way of solving this problem. For me, a way to solve the problem of showing the price, is to regularly change it as the price of bitcoin fluctuates. They can also have automated pricing screens to show the current price of the product so the owners would not need to change it themselves. But it's just my own opinion, I have a little less idea of how they really do it.