Hey Rain! Thanks for buying Mesh Edit.
If you hold CTRL/CMD while extruding, the faces will snap to a certain degree.
The amount they snap by is based on how zoomed in you are to the model, so if it's snapping too far out you can zoom in to control it better. Alternatively you can hold CTRL/CMD + Shift while extruding for fine snapping.
If you want a large number of equally sized cubes you can also extrude over a large distance and loop cut the extruded piece of the mesh with Shift + R.
Hope that helps!