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	$203.62	13.834%	$231.7888	$231.79	$231.80	$231.80
Purchase #2	$154.71	12.749%	$174.434	$174.43	$174.45	$174.40
Purchase #3	$95.30	5.601%	$100.6378	$100.64	$100.65	$100.60
Purchase #4	$101.61	7.140%	$108.865	$108.87	$108.85	$108.90
Purchase #5	$154.25	11.834%	$172.5039	$172.50	$172.50	$172.50
Purchase #6	$153.75	12.539%	$173.0287	$173.03	$173.05	$173.00
Purchase #7	$250.52	11.323%	$278.8864	$278.89	$278.90	$278.90
7 purchase totals =	$1,113.76		$1,240.1446	$1,240.15	$1,240.20	$1,240.10