Depends on what part of Canada and what the item is.
The sales tax applied on an item is a component of the federal GST (5%) plus whatever the provincial sales tax is.
For example, in Ontario, the harmonized sales tax is 13% (5% GST + 8% provincial):
17.99 x 1.13 = 20.33 (or after January 1, 2013, 20.35, as the penny will be officially retired).
In Nova Scotia, it's 15% (5% GST + 10% provincial)
17.99 x 1.15 = 20.69 (or post penny, 20.70)
In Nunavut, there is no territorial sales tax, just GST, so it's 5%:
17.99 x 1.05 = 18.89 (or post penny, 18.90)
If it's someplace else, you can look it up and do the math yourself