You are correct that there are not that many different tax combinations - BUT if a shop is selling a taxable product or service in a province that has 2 different taxes (PST - provincial sales tax and GST - general sales tax for example), then the shop needs to know and report how much of each different tax they collected. The reporting of PST and GST would go to different levels of government - so a shop would have to be able to separate them. A combined total would not work in these provinces for the hub manager, and it wouldn’t really work for the consumer either - since in CAnada consumers are accustomed to seeing each tax and its percentage as a separate line on any invoice (since we never include taxes in the price). Consumers look for these on taxable products.
I’m amazed at you @MyriamBoure, @oeoeaio and @CynthiaReynolds for your work on this. It boggles my mind.