You are using the "Commandes" module of Kentika?

Note that from January 1st 2013, the calculation method and rate of the Québec sales tax (QST) will change. It will now apply directly to the sale price excluding GST.

For details of this change, see the Revenu Québec website: http://www.revenuquebec.ca/en/entreprise/taxes/tvq_tps/calcul-taxes.aspx

The current version of Kentika (v2.0.0 r2) does not support the new taxes calculation method. You must use a single combined rate of 14.975%, as described in the section "Tax rates" of Revenu Québec website.