Rounding for different UOMs

Hi everyone, second post here.
I sell tiles and ceramics. We measure by square meter but sell in units.
For example a costumer tells me he wants 20 m2 and I calculate that he needs 54.64107643 and tell him he must get 55.
It would be great no to do this manually, So that I put in 20 m2 and the system charges for 55 units.