A lot of factors keep it from ever changing but I think it's just boils down to consumerism. Basically the same human psychology we play here with the 4.99 vs 5 dollars and not including sales tax in prices of stuff. Whatever way you can give a consumer a lower price before check out is ideal. It's not surprising America adopted this.

That steak isn't 18 dollars it comes with a 1.26 sales tax, .18 cent local tax, with a 3.6 tip. You'd feel too bad to get a soda if the steak was 23.04.