I clean my pennies by hand. Using Wright's copper cream, water and a toothbrush. It cleans really good. Never use Tarnex. It will give your pennies a weird color. I only clean the back side of the penny, since that is the side where the design is pressed on, while leaving an image of the front of the penny on the other, showing the mint year (most of the time).  I then store all my clean pennies in a glass jar with a couple of dessicant packets to absorb any humidity.