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	$166.60	3.750%	$172.8475	$172.85	$172.85	$172.80
Purchase #2	$91.36	13.652%	$103.8325	$103.83	$103.85	$103.80
Purchase #3	$45.68	13.719%	$51.9468	$51.95	$51.95	$51.90
Purchase #4	$104.61	3.652%	$108.4304	$108.43	$108.45	$108.40
Purchase #5	$148.45	8.297%	$160.7669	$160.77	$160.75	$160.80
Purchase #6	$11.68	10.422%	$12.8973	$12.90	$12.90	$12.90
Purchase #7	$49.64	3.733%	$51.4931	$51.49	$51.50	$51.50
7 purchase totals =	$618.02		$662.2145	$662.22	$662.25	$662.10