I can't imagine tipping anywhere for that, it's their job, and they're paid a regular wage, not a tipped wage. If you really wanted to do something, I'd say maybe $2 or $3 in the US. But I'm really against the whole tipping culture in the US. I mean I tip generously for food, etc, but I like the way it is done in Europe much more. I have a hard time tipping people who don't depend on tips as a part of their income. I certainly can't imagine tipping for it in Europe.