I have two U.S. coins. They total thirty cents. One of them is not a nickel. What are the coins?

Hello, mathbyte!
I have two US coins.
They total thirty cents.
One of them is not a nickel.
What are the coins?
I first heard this riddle on the playground.
I didn't care for the answer then.
I'm not too crazy about it now.
(But some of my friends laughed hysterically over it. .Go figure.)
"One of the coins is not a nickel", but the other coin is! . Nyuk-nyuk!