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	$12.67	9.771%	$13.908	$13.91	$13.90	$13.90
Purchase #2	$155.59	6.365%	$165.4933	$165.49	$165.50	$165.50
Purchase #3	$9.31	8.867%	$10.1355	$10.14	$10.15	$10.10
Purchase #4	$28.61	3.191%	$29.5229	$29.52	$29.50	$29.50
Purchase #5	$10.72	10.245%	$11.8183	$11.82	$11.80	$11.80
Purchase #6	$100.67	7.468%	$108.188	$108.19	$108.20	$108.20
Purchase #7	$180.37	4.263%	$188.0592	$188.06	$188.05	$188.10
7 purchase totals =	$497.94		$527.1252	$527.13	$527.10	$527.10