Actually, there are more approaches for rounded-edge boxes:
- Round-edged box 2
- Round-edged box 3
- Cheap round-edged box (vertex shader) (the best option is by @Fyrestar )
And moreover, there is a class of geometry, included in the distributive: jsm/geometries/RoundedBoxGeometry.js. Used here three.js examples and here White Gold (Reflector, custom geometry)