A long-distance phone call was rather expensive in 1958. However, a phone call within your same area code but with a different prefix would have cost more than a local call so a dime might have worked for that.
Candy bars were a nickel.
Maybe it was for a jukebox. Or maybe it was used to get a real nickel in change -- but it seems like a lot of work for that. It was probably cut down to fit into a key-chain good luck piece.
People do weird stuff to coins.