If you get anything that requires actual effort, a tip is appropriate. If you want that double shot of expresso mocha laitte with whipped cream, there are motions involved. It's multiple steps, they have to do it quickly and competently to avoid the line backing up, and they can screw it up if they're new, idiots, or don't care. Spare change for the trouble is probably sufficient, unless they get fancy with it and make a smiley face or something. Which is stupid, but hey at least they care and are trying, and that's usually with an additional buck plus the change.
But if you're just getting coffee then no. At least I don't think so.