Totally understand your point about making it visible -- shows people where their money is going instead of a smooth but obfuscated transaction -- but it's also onerous to have to do the math all the time.

I used to live in one of the richest counties in the US, and they had different tax rates in my city for eat-in, vs. takeout food. Also different tax rates for certain consumer staples. The solution was to carry an extra $20, not to do the math. And that gets abstracted away when you start using debit or credit all the time -- just lines on a statement.

Meanwhile, living in Australia, when I saw something in the store that said $5.50, I only had to make sure I had $5.50 in my pocket.