Without having visited your home to see your space in person, we're making some assumptions about the rounded edges you're referencing. We're assuming that the corners are not square in the area you would like to tile and you're not talking about a broad curve in this vicinity. If it is the corners that are posing a challenge, you can consider two potential options to work through this when tiling:
1. You can remove the wall board in this particular area and put in cement board, and in doing so create square corners. Cement board is a superior choice when tiling, so it would be a smart option that doesn't have to be costly to implement.
2. A skilled tile setter can do what is sometimes referred to as "buttering" the back of the tile with the setting materials, effectively floating the tile so that it compensates for a lack of square corners. This is a bit more challenging and requires an experienced person to execute it properly, but may be another option to consider.