From the US Treasury department website, the law on currency:
Defacement of currency is a violation of Title 18, Section 333 of the United States Code. Under this provision, currency defacement is generally defined as follows: Whoever mutilates, cuts, disfigures, perforates, unites or cements together, or does any other thing to any bank bill, draft, note, or other evidence of debt issued by any national banking association, Federal Reserve Bank, or Federal Reserve System, with intent to render such item(s) unfit to be reissued, shall be fined not more than $100 or imprisoned not more than six months, or both.
IANAL, but I think the key word here is “unusable”
And, the law on coin:
This question is addressed by 331, U.S.C. 18, which provides penalties for the mutilation of our coins. These penalties consist of not more than $2,000 or imprisonment of not more than five years, or both. This section generally applies to anyone who “fraudulently alters, defaces, mutilates, impairs, diminishes, falsifies, scales, or lightens” any coins circulating in the United States. It also addresses anyone who “fraudulently possesses, passes, utters, publishes, or sells . . . or brings into the United States, any such coin.” If you believe you know of such fraud, you should contact your local office of the United States Secret Service, which is responsible for investigating such cases.
I think the key word here is “fraudulent.” There’s some scratching on it, but not any fraudulent intent. Those “penny machines” that turn your Lincoln cent into a flat ellipse with some design imprinted on it are (IMO) probably not doing anything “fraudulent.”