I guess my question would not be how many bundles are left, but what PERCENTAGE of the roof is actually overage, savvy? 8 squares is unreasonable for a roof that is only 25 squares total, 8 squares left on a roof that is 80 squares shows a little bit of laziness or uncertainty about the layout, and 8 squares left on a roof(s) of 240 square is a sign of pure estimating talent! (approx 2%)
As the other roofers have pointed out, the roof bill is usually the total agreed upon cost of the new roof as stated in the contract. Period.
If the customer wants to parse the quoted cost BEFORE the job is done, that is his right. Asking the contractor for the credit for the returns on material and labor is his right but should be addressed PRIOR to the job ending.
Realize if you are the customer, you have agreed to a price which struck you as satisfactory in the beginning for the roof- and therefore, the shingle/labor returns are immaterial and left to the roofers discretion.
That being said, it is an unfortunate occurence of less than reputable roofers to PURPOSELY pad the material bill and process the returns as straight profit. This is flat wrong in my opinion.
Caveat Emptor still prevails right along with word of mouth.