Because of the crumbly nature of ceramic tiles, it is impossible to cut a large circular hole without breaking the tile. The best way to overcome the problem is to first select a coin that is nearest to the size required, and, placing it in position on the glazed surface. Score round it with a tile cutter. Make a clean cut across the full width of the tile, bisecting the circle, and with a pair of pincers gnaw out each of the semicircles. Finally fit the tile in place, rejoining it along the cut line. Provided that the cut is clean, the join will hardly show.