No, you can't convert like that. Most things will be charged a handling fee from Canada Post (extra brokerage and COD fee if you use FedEx or UPS). After that, everything will have PST and GST added.
Whether or not your item has duty, depends on what it is - you need to check with customs whether your item is a dutiable thing. For example, I've had to pay duty on flatware before, but not for toys. Duty is above and beyond the PST/GST., and the percent varies.
Again, depending on the item, it may have an "excise tax" if it's considered luxury. Jewelry and watches usually fall under that category. I believe it's around 12% extra for the excise tax - Customs recently converted to a flat rate for excise.
HTH!