28 November 2011 Interpretation Case No. 125136
It is pemissible both to compute the federal and provincial components of HST separately and round each component in accordance with s. 165.2(2), or to compute the combined HST first, and then so round.
The phrase "tax that is at any time payable" in subsection 165.2(2) is sufficiently broad to allow both rounding of total tax and rounding of each of the fderal and provincial part. As long as a registrant is consistent in its choice of method, and reports the tax charged, either method would be acceptable.