OK, managed to answer my own question. For future reference if anyone else needs to know, I'm posting a couple of pics so that people will know where the tabs are inside the case. Instructions are as follows:
1. Locate and unscrew single philips head screw.
2. GENTLY push in where tabs are indicated on one side of case and GENTLY pry open from that side while pushing forward toward the connector opening to get the back tab unhooked. You DO NOT need to pry it open with any tools, your hands should be sufficient.
Hints: You can see the front tabs in the connector opening, this should clue you in to which side is which as far as the tabs go. The case is very hard and not pliable at all so do be careful and don't apply too much pressure.
DO THIS AT YOUR OWN RISK!! If you have any reservations about possibly damaging your cartridge(s), DO NOT try to open it. Also, I only opened one game cart, so I can't guarantee that they're all the same inside.