The penny is no longer a viable coin, due to its lack of intrinsic value. Considering that per (https://www.measuringworth.com/uscompare/) the half cent had at least as much purchasing as a 2016 dime when it was discontinued in 1857, it seems counterintuitive to mint the penny when it is effectively useless on its own. Furthermore, it is fairly uncommon for people to count out exact change, particularly when pennies are involved.
See for a succinct argument which discusses these points as well as others.