Ironically enough, I called Lowe's and asked what their policy was. They said the first two cuts were free and they were $0.25/cut after that to a maximum of 10 cuts. So I thought, "Well I don't mind the $0.25/cut, but if they max me out at 10 cuts I'm only going to get two sheets and come back for a third sheet later".
So when I got there he asked how many sheets I needed and I told him 3, but I'll just take 2 because they won't fit in my truck unless they're cut. So he asked to see what I was trying to do and I showed him my drawings of the 4x8's and where I needed them cut. I made it simple for him, 12" shelves - cut this sheet 6 times every 12". For the box I had him cut at 22" four times, and the third sheet he cut at 14" a bunch of times. I will take it from there and make the rest of the cuts at home.
But to answer your question, yes he cut them perfectly for the box. We used a block so that they were all consistent cuts. I told him 1/16" either way would be ok as long as they were consistent. The shelves ended up at 12 3/16" or so, but consistently so what do I care. I helped him make the cuts and was there late, so there wasn't a lot of customers around. When we were done he said, "No charge for the cuts!" Of course earlier that day I spent $2500 on window coverings so that helped.