This assures that the added amount ($0.89) is 28% OF THE FINAL TOTAL.
Of course most (all? - anyone have a counter example?) sales taxes are computed (by law) as a percentage OF THE SALE PRICE, not as a percentage of the grand total. (Most Canadian provinces have TWO sales taxes, federal and provincial, and it is unconstitutional for one level of government to tax the taxes of another level of government. So sales tax as a percentage of the grand total would be unconstitutional here.)
However, I do have an example where the calculation should be done as above. Condominiums in BC must put a percentage of their TOTAL BUDGET into a continguency fund. Normally, managers find the budget by adding up all the expected operating expenses for the year (say $10). Then they have to add an amount (say 28%) for the contingency fund. If they just add 28% of $10 (makes $2.80) then the total budget is $12.80 and the contingency fund gets only $2.80/$12.80*100%=22% of the budget, violating the law! On the other hand, the managers in the condominium I used to be part of always did it this way. (Actually the legal requirement is only 10% so our condo always put aside 9%. But the law has no teeth. Managers do not even have to be licensed, yet.)
Robert, who is |)|\/| || Burnaby South Secondary School |\| |firstname.lastname@example.org || Beautiful British Columbia Mathematics & Computer Science || (Canada)