In the lotus lunar series (scalloped) the first two coins were sterling silver (92.5& Silver) and therefore were gst/pst/hst taxable. The third coins, the dragon was pure silver (99.99&) so it was not taxable.
There was a bug a while ago where the mint did end up charge you sales tax. Anybody who noticed, needed to call and get a refund on the taxes. It looks like they finally got around to refunding people without having to be asked. :)