This OpenSCAD code is just a few lines that will make a cube with rounded corners. 

It works very like the ‘cube’ statement. This code is a module so, instead of the call looking like “cube ([123, 234, 345]);”, the call would be “nice_cube (123, 234, 345, 4);”. The first three parameters would be the same, and the fourth is the radius of each rounded corner. 

I've now used this code in several models I've made and it suits me very nicely. I've included a picture of “PiZeRadio” which is my most recent model using a cube with rounded corners. 

The .scad code file includes a demo of the module in use, creating the screen shot from OpenSCAD and the .stl model.

Have fun!