I just went through something like this with an architecture dataset I was toying with, though it was hundredths of feet, not sub-millimeter rounding.
The default coordinate reference generally preserves thousandths of meters, though some dip into the ten-thousandths. Unfortunately, it varies by coordinate system (max resolution across the entire mappable space).
The only way to change ArcGIS coordinate reference behavior is to take proactive ownership of the coordinate reference used in your data conversion. The first step here is to read (and understand) the Understanding Coordinate Management in the Geodatabase White Paper. Then you need to determine your actual XY/Z/M coordinate reference range requirements and determine the exact offsets and scales necessary to accomplish them. At that point, you can create a Feature Dataset which uses these values. And then all data conversion should go though that Feature Dataset. Since spatial references are immutable, once the feature class is created inside the FDS, you can drag it back out to the parent file/enterprise geodatabase.
You should also consider whether tenth-millimeter precision is actually necessary. I can assure you that the carpenter building my retirement home is not going to achieve better than 1/16" precision, possibly as little as 1/4".
- V
