After printing the two half dices put an iron ball (8 mm) inside and glue them together. To take care of the right position, look at the numbers 2 and 5. 

If you want and have more talent than me, you can color the cubes.

Update RoundDice_2:
Some small changes in the model.
Added 3mf file to get better printing results.
Added gcode-file for Prusa mini.