The way custom brushes work (that is what the extension uses) makes it impossible for this extension at least to round the pattern. Someone requested this previously and when I tried to get it working I'm pretty sure there would always be a weird gap where the corners of the square patterns would be.
Maybe in the future if aseprite supports custom tools I could make a dithering brush tool that would work much better. For now though I don't think it is possible without modifying source code.
