IF you mean "what is 102.1604043 mm^3 to the nearestcubicmm", not "mm", then the answer is 102 cubic mm., of course. 102.1... isbelow102.5 so it is nearer 102 mm than 103 mm.

If you mean to take the cuberootof 102.1604043 and then ask "what is it to the nearest mm.", it is easy to use a calculator to see that which is larger than 4.5 mm and so is 5 mm, to the nearest mm.