I think tip jars at a convenience counter is crap. This is a fairly recent phenomenom in the last few several years. Let me clarify...
Tips generally are for waiters and waitresses. They make a COUPLE of bucks an hour, far below minimum wage. Tips ARE their wages. It gives them incentive to be quick and efficient, and it rewards those with the best performance the most.
Somebody standing at a counter, taking an order and giving to someone else, then moving on to the next should not be tipped imo. They are getting paid to do a simple job. Take an order, and pass it to the kitchen. I worked several years at one such place, so don't think I'm being harsh. I didn't get, deserve nor want tips for such a position.
Now, a waiter/waitress has to set your table, get your drink order, bring that, get your food order, bring that, clear the table as dinner goes and refill drinks, bring extra napkins, silverware, to-go boxes, etc. There is a lot of interpersonal stuff going on there, and people can be demanding. You can sit there for 3 hours ordering an occassional drink, and they still have to oblige you, though your bill is not going up quantitively enough to ensure a tip worthy of their effort. THAT deserves a tip. And I applaud them, as I could not put up with the assholes I've seen at restaraunts and bars, and I very much appreciate a conscientious server, and I tip very well accordingly.
But, to take a damn 20 second food order and have someone else make it, and hand it to me, and they are no longer affecting the outcome of my dining experience... please.
Here Here for Severe Clear!