Tax Rate Derivation for Canada in 11.5.10.2

Hi,

We are on 11.5.10.2 and for one of the transactions the customer address is Toronto, ON and the tax code is GST_HST and tax rate should be 13%.  We have defined the tax code 'GST_HST' without any tax rate as the same tax code should be used with a different rate for a different customer based on the location.

How do we derive the tax_rate of 13% in this case without actually defining the tax_rate in the tax_code 'GST_HST' definition.

Appreciate your help

Thanks & Regards,

AK