Michael Williams, in a post about the proposal to put Ronald Reagan on the dime, notes that eliminating the dime and replacing it with an 18-cent coin would make our system of change 17% more efficient. He wrote about it first here.
Apparently doing this would reduce the average number of coins needed per transaction from 4.70 to 3.89. It would make figuring change a pain, though.
I agree with his thoughts that replacing FDR with Reagan on the dime just doesn’t make sense, though.