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	$9.31	12.670%	$10.4896	$10.49	$10.50	$10.50
Purchase #2	$127.72	5.406%	$134.6245	$134.62	$134.60	$134.60
Purchase #3	$71.34	4.110%	$74.2721	$74.27	$74.25	$74.30
Purchase #4	$208.89	5.458%	$220.2912	$220.29	$220.30	$220.30
Purchase #5	$40.58	12.287%	$45.5661	$45.57	$45.55	$45.60
Purchase #6	$13.33	6.295%	$14.1691	$14.17	$14.15	$14.20
Purchase #7	$52.85	3.536%	$54.7188	$54.72	$54.70	$54.70
7 purchase totals =	$524.02		$554.1314	$554.13	$554.05	$554.20