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	$59.89	12.172%	$67.1798	$67.18	$67.20	$67.20
Purchase #2	$235.70	9.523%	$258.1457	$258.15	$258.15	$258.10
Purchase #3	$139.25	9.513%	$152.4969	$152.50	$152.50	$152.50
Purchase #4	$101.82	4.521%	$106.4233	$106.42	$106.40	$106.40
Purchase #5	$21.72	3.589%	$22.4995	$22.50	$22.50	$22.50
Purchase #6	$116.80	13.593%	$132.6766	$132.68	$132.70	$132.70
Purchase #7	$145.38	5.538%	$153.4311	$153.43	$153.45	$153.40
7 purchase totals =	$820.56		$892.8529	$892.86	$892.90	$892.80