The following modification changes the way OSC calculates taxes so that it gets compatible with Canadian compound tax calculation (especially in Quebec). It shows taxes calculation on two lines as required by many canadian province laws.

I think there is at least 4 mods published on this site that does this and none of them did fit my needs. The following modification should allow your OSC store to calculates GST and PST on seperate lines without making any rounding or calculation errors. I've sucessfully implemented this on various versions of OSC 2.2 and Creloaded carts.

This mod does not involve any hardcoding of tax values in ot_tax.php and relies on the proper way of configuring Canadian Taxes as described by Peter Mosier in http://www.oscommerce.com/community/contributions,1124

I'd like to thank Peter Mosier for the very clear instructions on setting up Canadian taxes in OSC. I've included an edited version of his work in this contribution (especially useful for setting up compounded taxes for Quebec). I'd also like to thank Nick Cloutier (Contrib #5399) for inspiring me on the right way to do this.

This mods assumes the following in your store setup:

- All products are taxable in your store
- All products have the same tax class (ie: taxable goods)
- Display price with tax is disabled in your store configuration
- Taxes are based on delivery address, not billing address
- Same tax rates apply on shipping fees than tax rates applied on ordered products
- Your order_total configuration is as follows (in Admin/Modules/Order Totals) :
1. Sub-Total
2. Shipping
3. Tax
4. Total

If your store configuration differs from what's mentionned above, you can try to install this module but tweaking might be necessary.

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