Kaleboutwest your insight on judaism is most welcome.
peacefulpete: "Especially the way it is written with the assumption of the image on the coin."
This is where I was getting at. The story is told by Mark, and then mirrored by Matthew and Luke, but "Mark" has no idea that it would be very unlikely that around 30 CE there were coins in daily circulation in Judea with the effigy of Caesar. "Mark" seems to be ignorant that the carrier of such coin would become ceremonially impure. Jesus may well have taught "give Caesar what belongs to Caesar" [pay your taxes to the Roman authority ] but "Mark" is just making up the use of a denarius to illustrate that point, probably because "Mark" (whoever was the author of that gospel) probably never set foot in Judea.
"Mark" probably wrote at least 4 decades after the fact, with third or fourth hand knowledge, to a roman audience, in Rome.