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	$111.74	6.668%	$119.1908	$119.19	$119.20	$119.20
Purchase #2	$158.71	7.628%	$170.8164	$170.82	$170.80	$170.80
Purchase #3	$221.93	12.422%	$249.4981	$249.50	$249.50	$249.50
Purchase #4	$127.33	8.152%	$137.7099	$137.71	$137.70	$137.70
Purchase #5	$81.76	8.852%	$88.9974	$89.00	$89.00	$89.00
Purchase #6	$176.74	5.145%	$185.8333	$185.83	$185.85	$185.80
Purchase #7	$85.43	6.653%	$91.1137	$91.11	$91.10	$91.10
7 purchase totals =	$963.64		$1,043.1596	$1,043.16	$1,043.15	$1,043.10