Unless there's a really good reason not to, you ought to be tipping at least a couple bucks an hour. I'm sorry, but these guys are working for minimum wage, and it won't kill you to throw a white chip out there every once in awhile when you've got a max bet out.
There's really no good justification for it either. Your refusal to tip doesn't hurt the casino, only the dealers, and it makes all counters look bad when you get tossed and haven't ever tipped.
That said, I think $5 an hour is more than fair to tip, even for a black chipper.