Well, after playing some more I realized that I didn't actually have the mines. I thought I did when I cleaned out the sewers. After climbing the long ladder (in the hallway in the dark), I thought I picked up 2 mines, but they weren't mines after all.
I eventually found the area that I was missing (off to the side of the main square where the 2 flags are hanging). The mines were located at the end of that area.

After getting the mines I was able to use my mouse wheel to go to them, and then simply had to throw 3 of them under the tank's tracks (they had to be placed pretty closely under the tracks, or they wouldn't explode). Also watch out that you aren't too close then they go off, or you'll take damage as well.