To properly cut a wire tie, grip the tie where it exits the head, stretch it slightly by gripping with wire ties and and bend it down.
Then clip it flush with the wire tie head. The cut edge will retract inside the head just enough to give you a smooth edge.
For narrow ties, try a toe nail clipper. The curved blades of a nail clipper will put a rounded edge on the cut end of your tie, eliminating sharp corners.