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	$124.89	11.521%	$139.2786	$139.28	$139.30	$139.30
Purchase #2	$230.29	11.302%	$256.3174	$256.32	$256.30	$256.30
Purchase #3	$104.87	6.337%	$111.5156	$111.52	$111.50	$111.50
Purchase #4	$114.81	11.164%	$127.6274	$127.63	$127.65	$127.60
Purchase #5	$63.39	12.682%	$71.4291	$71.43	$71.45	$71.40
Purchase #6	$151.67	13.472%	$172.103	$172.10	$172.10	$172.10
Purchase #7	$44.56	10.355%	$49.1742	$49.17	$49.15	$49.20
7 purchase totals =	$834.48		$927.4453	$927.45	$927.45	$927.40