What Two Coins Make 30 Cents and One of Them Is Not a Nickel?

This tricky riddle was featured on the American television show "Scrubs." J.D. poses the question to the Janitor. Instead of coming up with the simple answer of a nickel and a quarter, the Janitor researches coin history at the library and determines that the answer is a penny and a rare, out-of-mint coin that costs 29 cents to a specialty collector.