Can toilet paper stop a bullet?

Any amount of mass, if sufficient enough will stop a bullet.

One or two layers of TP will not stop a bullet. A single roll of TP likely won't either. But, if you were to have several (maybe 20-1000) rolls, eventually a bullet will transfer all of its kinetic energy to the previous rolls of TP and run out of energy.

How many rolls (the thickness) that would be needed depends on the bullet's size, velocity, composition, etc....