I would say go ahead a try it. If the clerkling gets all confused, slip her a $5 spot. That'll help her to "understand"! =) I've never had any problems, however, without tipping. They almost never look. Why should they? Some stranger wants to put free points on someone else's card? Can't imagine it's an issue. Now, if you're an ADT junkie like I am, I respect how they could be an issue. For the sake of this thread, I'll leave it as "You'll have no problems".