The problem with this, and almost every other fee, is that the customer sees one price, but must pay another. In Scotland (and many other countries) even tax is included in the price. I went to a shop, choose a £10 item, and prepared to pay with a £10 bill + change, and got a strange look.
If something is going to cost $21.57, I'll make my decision based on that, but I hate to see $19.99 when I can't pay $20 for it and be on my way.
The fee isn't truly hidden, but it's intellectually dishonest not to price goods and services as they will be charged.