I currently have three outlets in my garage, two in the ceiling and one in the wall. They all are on the same circuit. I want to tap off of the wall outlet and make two additional outlets located near my power tools. I'm using metal switch boxes and 1/2" metal conduit both mounted and ran outside the wall. Should the two metal boxes be grounded when making the connections inside?

Absolutely!!!!!
You be running three conductors in that pipe. One black, one white, one green and you should change that wall receptacle to a GFCI.
If you plan to use powertools and have a workbench there in your garage I recommend a separate 20amp circuit for your workbench also GFCI protected.