CAD tip # 14351:

Double-click on the parts list in the drawing (or right-click and select "Edit Parts List"), then right-click on the column name and select Format Column from the context menu. Switch to the "Apply Units Formatting" option and verify the Units and Decimal Marker settings. In the "Format Column" dialog, then toggle the trailing zeros suppression on the "Trailing Zeros" icon:

You can also, of course, change the Precision of the displayed units, but there you may get unintentional rounding (it will restrict all decimal digits above a specified count, not just zeros).