Coin 1/4" Hex Screwdriver bit

STL includes supports for printing at a 45" angle. You may need to file down any nibs left over from the supports.

It's designed to be a tight fit to minimize play in the coin. This requires a bit of flex in the material, so avoid particularly brittle filaments. To get the penny in, mount the bit in a handle, hold the coin in place, and press hard against a stable surface. Alternately, hold the bit in a vise and give the coin a good smack with a hammer. 

The include Fusion file is parameterized so it should be easy to modify for different types of coins.