Altimeter tolerances for larger aircraft are normally laid down in the maintenance manual, and have tightened up considerably with the introduction of RVSM. For smaller GA aircraft the tolerances are significantly larger, the LAMS gives no guidance on the actual limits and most companies make up there own procedures, normally based on the previously referenced FAR.
Just for info there IS a field adjustment that can be carried out on most GA altimeters by a suitably licensed engineer, and that is to adjust the BARO scale calibration, this is normally the problem with altimeters on the ground and once adjusted properly will normaly fall into limits at altitude.
Hope this helps