minkowski() is kind of slow for just generating round cubes. hull() however seems to be much faster. The module works by applying a hull() around eight spheres which are spaced apart to make the cube's shape. The spacing automatically compensates for the outer rounding radius. You can try it out in customizer. To use in your own projects, you don't need the "customizer" named variables. The sample file contains a 10x10x10 cube, 1mm rounding radius, 32 facets.