A rule of thumb for calipers, mics and other instruments with a graduated readout (i.e. digital, vernier scales, etc.) is they should be accurate to ± 1 graduation of their scale. For example, a caliper whose smallest increment of reading is .0005" should be accurate to ±.0005"
As the others have mentioned, you can downgrade your instruments by calibrating to looser tolerances, but they should be noted with their calibrated accuracy. The caliper above could be calibrated to ±.001" if it's not used for measurements that require finer reading, but it should not be used thereafter for finer measurements unless recalibrated and proven capable of doing the measurement accurately.