Cheating in anything at work, even in "just for fun" contests, is not a very bright idea and I would not advise anybody do it even as a joke.
More and more fortune 500 companies have ethics requirements that even extend to their employee personal dealings. In some cases it goes to government contract eligibility; in other cases it's just fear of government punishment in the form of clampdowns such as IRS audits, sarbanes oxley, etc.
Why fortune 500? I think it's because big companies have the most to lose if they screw up and lose a couple of government contracts, or worse yet, get disqualified from future contract eligibility. Hence the no smoking rules and so forth.
In more and more companies, if you get caught perpetrating fraud in your professional life or even your after-hours life, even something as simple as fudging your steps for a health contest, or say your name ends up in the newspaper for fraud, DUI, leaving the scene of an accident, shoplifting, cheating on your wife, etcetera and evidence exists that you are guilty, you could be let go from your job. If you're high enough, you'll just be "asked to resign" so that the evidence doesn't come out.
About the only thing I know that still won't jeopardize your job is being a bad tipper. But give it time.