I have my Model Info > Units set to return a whole of mm, so if the dimension is not a whole number SUp rounds it to the nearest whole number, but it adds a ~ to warn you that the figure is 'approximate'***...
1.0mm ==> 1
1.2mm ==> ~1
1.9mm ==> ~2
1234.0mm ==> 1234
1234.5mm ==> ~1235
***I find that I don't need to report dimensions etc to anything smaller than a 'mm'... You can if you like...