I assume you're talking compressed air. You "can" store anything in the tank up to the rated pressure. That said if it is an oxygen tank marked as "oxygen" (or has a white shoulder) I doubt any reputable fill shop would fill it with compressed air. Buy the proper tool for the job, get a new or used scuba tank.
Whether a shop would fill it or not may not matter. In all likelihood the connectors between an oxygen tank and a compressed air tank are incompatible, deliberately, so you could need an unobtainable adapter.
The connectors are different, and for liability, I doubt a company would fill it. The CGA connector is a 580 for air, and a 540 for oxygen if I recall. Generally a O2 tank is filled to 2200 psi, so that is pretty low to use as a filling source. SCBA tanks at 4500 psi are the way to go.
