I hesitate to even mention this because first I don't really know what I'm talking about and second I don't want to hijack your thread into another topic but ... is it "legal" to do that? My understanding is the credit cards don't let you in general. Here is a topic discussion about it:
Having said that, I've seen SO many businesses do it anyway, there must not be much enforcement on it (assuming my assumption is correct) by the credit card companies.
Feel free to correct me... like I said, I don't really understand the rules myself. And because of that lack of understanding, we've never done it.