Snapping selected actors to grid?

Is there a way to snap selected actors to grid? What I have are buildings composed of modular walls. I duplicated and rotated the buildings. Now all of the pieces are off a little bit from the round-off error introduced from the operation. What I need is way to snap all the individual pieces back onto grid. If I select all the pieces at once and perform the snap to grid function, it only snaps the last item selected. So I’m having to select each piece one at time and perform the snap. This gets really old in a hurry – especially when you have a hundred actors.