Is a 1972 penny with tails on both side but one side is backwards worth anything?

It sounds like you may have what's known as a brockage error. These can be very valuable -- hundreds of dollars. But you need to get it evaluated first-hand by an expert, because if it turns out to be something altered after the coin left the mint, then it will be worthless. And without a first-hand examination, it's impossible to tell. I recommend you visit the http://www.anacs.com website and check their show schedule to see if they will be in your area in the near future. They provide free professional appraisals and accept coins for certification right at the coin show. Good luck! Dan