The problem: the dollar is almost global in its usage. The penny may not be important to the US, but it dam well is every where else where dollars are still in use frequently, along side, or in place of the local/native currency.

Getting rid of the penny will have implications, getting rid of more coins would endanger the use of the dollar globally.

There is still a large portion of the world where 100 dollar bill and a Rolex will get you home safely.