It's more trickier than that, Sigurd. Augustus did hold a census before year 0, but not in Judea. The Romans did not order a census of citizens of client states; that's not Roman territory proper. Citizens of client states were not taxed by Rome, thus no reason to hold a census.

And Galilea was never a Roman province; Joseph as a citizen of Galilea would thus never be subject to a census.

And it wasn't standard practice for people to travel to the censor either; it was the censor who travelled to the citizen.