I have found a 2001 D nickel that the obverse is 3% or so off center, with the reverse on center. What caused this?
That is called a MAD. This coin exhibits what at first appears to be an off-center strike; however, the opposite side of the coin is in perfect alignment. This error occurs when a die (usually the hammer die, but occasionally the anvil die) is offset in any direction. In order for the error to have any significant collector value, it must have a portion of the design missing. Typical examples of this error type will range between 2% to 5% Off. This error is often called a Misaligned Die, or MAD for short Credit: CONECA Speedy
It might sell on ebay. While I agree that 3% isn't something I would bid on, I've seen some with a small ammount off sell for a buck or two. Speedy
Errors are not my cup of tea, but this nickel is nice BU, so I will stick it in a 2X2 and keep it. I don't sell US coins, just hoard them.