I know your code work to get the cost, GST value and PST Value.
To do it you use the reversed rate value 1.15025.

Do you know how to get this value(1.15025) from the taxes rates ?
In my case I have to do this for all provinces.

Price incl.tax/((1+GST/100)*(1+PST/100)= Price excl.tax

115.03/((1+7/100)*(1+7.5/100))= 100