Make 2 variables for the amount of pixels in each incrememnt you want objects to snap to named snapX and snapY.
Then when you are placing the object, set it to Self.X - (Self.X % snapX) and Self.Y - (Self.Y % snapY)
The % operator is called modulo, modulus, mod, etc. It gets the reainder after a division. So youre subtracting the amount of pixels the object is between 2 snap points, and setting it to the lower one.