To save the enviornnment and money, don't top off your gas tank. You may have the urge to round up those odd dollar amounts at the gas pump, but topping off your gas tank doesn't necessarily mean the gas is going in to your car's tank. In fact, according to the Environmental Protection Agency, once your tank is full and the gas nozzle automatically clicks off, you are just feeding back gas into the station's tanks. In order to prevent gas vapors from escaping and causing air pollution, gas stations are equipped with vapor recovery systems that feed back the gas vapors into their tanks.

In addition, overspillage of gasoline is harmful to breathe and contribute to bad ozone days. Plus, you pay for the gas that overspills and eventually evaporates or leaks in to the ground.

For more reasons not to topoff your gas tank go to EPA.gov