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	$173.53	3.640%	$179.8465	$179.85	$179.85	$179.80
Purchase #2	$100.29	8.409%	$108.7234	$108.72	$108.70	$108.70
Purchase #3	$41.47	7.137%	$44.4297	$44.43	$44.45	$44.40
Purchase #4	$84.85	6.354%	$90.2414	$90.24	$90.25	$90.20
Purchase #5	$33.40	11.168%	$37.1301	$37.13	$37.15	$37.10
Purchase #6	$166.35	11.323%	$185.1858	$185.19	$185.20	$185.20
Purchase #7	$222.90	9.491%	$244.0554	$244.06	$244.05	$244.10
7 purchase totals =	$822.79		$889.6123	$889.62	$889.65	$889.50