Cash registers or any other interconnected systems, get blown up because you don't have enough bonding, not because you have ground loops.
In one particular building (actually 3 store fronts opened up to be one) we ended up actually pulling a bonding wire along with the LAN cable to positively bond all the frames together. That is the definition of a ground loop but it was what it took to stop us from replacing system boards and LAN cards a couple times a week in the summer.
