Even if there had been a census it would have been a distributed task for the tax collectors. The Romans never had the entire population ordered to appear at a country's capital for any reason.
"Remember the 2010 US Census when 300 million citizens had to go to Washington D.C. to fill in out a questionnaire ?"
And the most damning fact? Those Romans kept records of **everything**.
No Roman record of this "census" thing at all.