NO, you should NOT use tape over a postage stamp, because the tape can invalidate the postage and the mail would more than likely be returned to the sender. Here's what the U.S. Post Office says: , you should "Affix your stamps securely, but do not put tape over the stamp(s) — this invalidates the postage."
Just try using a glue-stick or glue to secure a stamp to an envelope.
If the post office allowed tape to cover stamps, you could just keep reusing stamps because the postmark would only be on the tape (not the stamp itself).
If you need new stamps,you can buy stamps online at Stamps.com