I've seen that in places here in NY. If I have a dollar or two on my wallet, I'll hand it to Katy and tell her to put it in the jar.

I NEVER put money in the tip jar at the little Chinese takeaway that we used to go to. The reason: all the people who worked there were members of the same family and they owned the place :) However, when we had the food delivered, we always tipped the delivery guy a couple of dollars. Different story...