Another way to do this is to render your animation, then go to the video sequence editor. Add your rendered images or movie, press N and go to the drop down menu options, scroll down in the filter section and check the option to play the videoactive clip backwards. Go back to VSE press control F12F12 (to sequence render, again), with the backwards box checked and this will render your animation in reverse.
improve clarity by adding the section which the mentioned option's checkbox is located. also slight grammar fixes