NY Rat:
If you know the length, most hardware stores will shear them for you at none or minimal charge. For PVC they use a tree pruning type of ratcheting cutter to cut the PVC, and they usually ream and round the edges as part of the process.
Otherwise use a knife and sandpaper for rough edges.
One way to keep your cut square is to take a straight piece of paper and wrap it around the PVC at the point you will be cutting. Take a marker and lay down a mark using the edge of the paper as your guide. Cut part way into the PVC, turn 90 degrees and cut part way thru, turn 90 degrees,-------etc., until you have cut entirely thru the piece. You will have a much more square cut. When capping PVC or glueing a threaded fitting on it, perfect square shoulder cuts are not that important as the permanent cap is friction fit and glued, and the other end is either open, friction fit capped, or has a fitting glued to it for a screw on cap.
Good luck!
Bountyhunter