Multiple choice with round checkbox

This is by far the weirdest question I ever have seen on these forums. You want to go against the universal rule that checkboxes (square) are used when multiple choices can be marked, and radiobutton when only one can be marked? Are you sure that all your learners are unaware of that universal rule? If that is not the case you will really confuse them.

To give you an answer: you can have all square check boxes, by always chosing multiple answers, and choosing only one answer when necessary. That would at least not be as illogical: you are trying to hide whether there is one or multiple correct answers. Do never use radiobuttons when you have multiple correct answers, some of your learners will be upset.