When I send an .igs file to a machine shop for a machined part creation is there a built in tolerance or do I accept the tolerances of the NC machine doing the milling?
you can add tolerances to your dimensions in your model sketches and that info should
pass into your iges file.
The best you can do is pick the system the file will be exported to, see image. You can get to this through the options button in the save-as dialog.
Retrieving data ...