Aaaah, sorry. Now I understand your point.
I don’t know if something generic exists because I normally use decimal to DMS converters. The most frequent Northing Easting converter types I have seen so far are just based on UTM or NATO coordinates formats, for example:
This one accepts UTM using decimals, so it should avoid the precision problems, but is working in meters only. Is it possible that book was using feet instead?
If that´s the case maybe there are other similar converters, like the following which is aparently supporting the american units, but to be honest I never used it and I just found it after a quick google search:
https://www.earthpoint.us/convert.aspx
Cheers