tipping cashiers in AC poker rooms

[Eponymous]

I know...another tipping thread. But this is a very specific question. I usually tip a buck or two to the cashier when I cash out, but I get a different yet consistent reaction depending on the casino. At the Borg, they set the dollar on the side, make no expression whatsoever, and don't say "thank you" or anything else. While at the Taj, Caesars, and I think others, they seem very appreciative. I've even seen some of them fish for a tip a little bit by asking how the evening was, if you won, etc. Is there a policy at the Borg that they don't personally keep the tips, but they don't refuse them either as not to offend? Maybe they go into a pool or something and are told not to thank people so that it's not encouraged. Anyone else notice this difference at the different AC casinos?