Ragged edges after using split tool in Modeler

Hey I am just learning to use modeler and trying to make a toaster from the tutorial. The problem is that after using the split tool, the edges of the different parts are jagged. I've also tried increasing the resolution of the object, up to 6 times, but it doesn't have much effect, whether I'm using a square, a sphere or something else to cut out the shape. Does anyone know why this is happening and what I can do about it?