This was not a miracle of creation (Jesus did not create the coin out of nothing) but a miracle of providence--controlling and directing natural processes to produce a desired result, that otherwise would have an almost infinitesimally small probability of occurring.

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8