Our current US physical currency system is a mess and is an unnecessary waste of money and time in our modern society of credit and debit cards and new technologies like paying by phone.
The Federal Reserve should therefor retire the penny, nickle, quarter, and one dollar paper bill; meanwhile the only coins that would be produced now would be the dime, half dollar, and dollar coin.
Below are two links to John Green's discussions as to why the penny, nickle, and one dollar bill cost too much to produce to justify keeping them in circulation. If any presidential administration were actually serious about cutting government costs, this seems like a no brainer.
Kill the Penny and Nickle - https://youtu.be/77C47XYm_3c
Kill the Dollar Bill - https://youtu.be/SHC2pqxdjlQ