The jargon spelling is technically (according to the dictionary) both ways. Wikipedia (which I don't generally like) lists "casino tokens" as "chips, checks, or cheques." The Las Vegas Advisor, however, preferred the spelling "cheques" as opposed to "checks," although they allowed "checks" in the title of the question without correcting the author in the article. In a back-and-forth on WoV, some people said they used either spelling. I'd say "cheques" outnumbered "checks" about 2 to 1, although evidently non-value cheques is its own term regarding blackjack and roulette tournaments, so some people avoided spelling it "cheques" for that reason. The consensus, and I agree, is that "cheques" is to be preferred as the spelling, but "checks" is not technically incorrect. The managerial person I spoke to also said I should have spelled it "cheques" to avoid confusion, which I reported.
Editor Bob