Based on what you said I assume you are leaving the toilet in place and tiling up to it. Bad idea. Not only will it be difficult to shape the tile to the contour of the toilet and make it look good if and when you ever replace the toilet the new toilet base will most likely not be the same shape as the old one. Hence, you have a problem. Pull the toilet, tile a couple of inches under it, better yet an inch away from the drain. Grout the tile, reset the toilet and then caulk with 100% silicone if you like. You'll be glad you did it like a professional especially if you ever replace the toilet.