This version computes by adding GST HST and PST to a base
price.  It currently does not work in reverse given the
final price working backwards to get the taxes and base
price.  In other words it will not tell you the sticker
price to make something come out even after taxes are added.
However, it has a spinner that lets you approximate that
function.
Just select the vendor and buyer's province, enter the
amount of the sale and hit calc.  You can adjust the sale
amount with a spinner.
You can also work backwards, filling in the total amount and
hitting calc to work out the original amount of sale.
To install, Extract the zip download with WinZip, available
from http://www.winzip.com (or similar unzip utility) into
any directory you please, often C:\ -- ticking off the "user
folder names" option. To run as an application, type:
java.exe -jar C:\com\mindprod\canadiantax\canadiantax.jar  BC
adjusting as necessary to account for where the jar file is.
CONFIGURING THE DEFAULT PROVINCE
You can configure the province CanadianTax starts up with.
On the command line, just place the 2-letter province abbreviation
as the last thing on the line.
The the only abbreviations it accepts are:
BC : British Columbia
AB : Alberta
SK : Saskatchewan
MB : Manitoba
ON : Ontario
QC : Quebec
PE : Prince Edward Island
NB : New Brunswick
NS : Nova Scotia
NL : Newfoundland/Labrador
YT : Yukon
NT : NWT
NU : Nunavut
For Applets, modify the
<param name="prov" value="BC">
in canadiantax.html. You will have to download canadiantax
and set up your own modified webpage.  You can't modify the
Canadian Mind Products website since it is shared by
everyone.
WARNING!
********
Quebec and Prince Edward Island use a dishonest ploy to make the
provincial sales tax sound lower than it really is.  Unlike all the other
provinces, provincial sales tax is computed not only on the original sale
amount, but also on the GST.  This means Quebec's nominal 7.5% tax is
effectively 7.875%, and Prince Edward's nominal 10% tax is effectively
10.5%.  The Canadian Tax Calculator shows the honest, effective rates, not
the crooked nominal ones.