I am not sure if you have ever worked for tips, but in any casino, most employees work for minimum wage or something slightly higher than that.
It isn't customary to tip for every little thing, but if you are buying a lot of chips, or you feel the cashier cage attendant went our of the way to find you something, i would advise that you take care of the people who take care of you.
I always tip and I tip a lot more than i should, but i think that stems from me working in a casino enviroment for 13 years. i think it is in my blood.
hope that helps