Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$19.71	7.468%	$21.1819	$21.18	$21.20	$21.20
Purchase #2	$36.29	4.506%	$37.9252	$37.93	$37.95	$37.90
Purchase #3	$170.42	3.645%	$176.6318	$176.63	$176.65	$176.60
Purchase #4	$14.47	6.670%	$15.4351	$15.44	$15.45	$15.40
Purchase #5	$52.58	3.568%	$54.4561	$54.46	$54.45	$54.50
Purchase #6	$177.43	8.544%	$192.5896	$192.59	$192.60	$192.60
Purchase #7	$128.43	12.344%	$144.2834	$144.28	$144.30	$144.30
7 purchase totals =	$599.33		$642.5031	$642.51	$642.60	$642.50