Final answer:
A chisel. A chisel would be used along with a hammer to cut a rounded-off nut on a vehicle by placing the chisel against the nut and striking it with a hammer.
Step-by-step explanation:
The tool that would be used along with a hammer to cut a rounded-off nut on a vehicle is a chisel. A chisel is a hand tool with a sharp cutting edge used for shaping, cutting, or carving hard materials such as wood, stone, or metal.
To cut a rounded-off nut, you would place the chisel against the nut and use the hammer to strike the chisel, applying force to cut through the nut and remove it.
Using a file or a screwdriver would not be suitable for cutting a rounded-off nut, and a punch is typically used to drive or remove pins or rivets.