Representing a sphere on a battlemap

Hey there. I'm mapping out a small planetoid for a Pathfinder game and was having some concerns with how to represent a sphere on a square grid. Unfortunately I've got to stick with squares (or my players are likely to complain I think), but I've come up with something that might work, and will probably meet the levels of simplicity that my players will be okay with.

My idea is essentially to take the surface area of the sphere, and get the square root of that, use the root to make two sides of a square, and then divide that square as evenly as I can into 5x5 inciments, saying that each edge of the square loops back to the other side. Probably nowhere near a perfect representation of a sphere, but it could work. What do you folks think? Does anyone have any other easy ways of doing this?