The tank in the mall can give you some extreme points IF you know what to shoot at and create combo's out of:
-6 side guns (3 on each side of the tank)
-1 gattling gun (the gattling gun on top of the tanks primary gun)
-1 primary gun (it's obviously the big gun on the tank
-2 rocket launchers (on either side of the tank)
These parts of the tank you can start shooting at right away, but there are 4 other places of interest that only open up once certain parts of the tank are destroyed:
-2 back rocket launchers (when you thought they were done, there's more, located on the back part of the tank)
-2 more gattling guns (inside the tank, last part of tank to destroy)

Note that the rockets that are being fired at you can be destroyed:
-Large rocket (that come from the side launcher's of the tank) These take more than one bullet to destroy.
-Groups of orange rockets (come from the back launchers of the tank) These can be taken out with one bullet, but be careful and fast.