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	$245.45	13.382%	$278.2961	$278.30	$278.30	$278.30
Purchase #2	$82.76	6.447%	$88.0955	$88.10	$88.10	$88.10
Purchase #3	$205.66	4.124%	$214.1414	$214.14	$214.15	$214.10
Purchase #4	$157.60	9.594%	$172.7201	$172.72	$172.70	$172.70
Purchase #5	$39.83	10.638%	$44.0671	$44.07	$44.05	$44.10
Purchase #6	$17.45	5.338%	$18.3815	$18.38	$18.40	$18.40
Purchase #7	$179.65	3.247%	$185.4832	$185.48	$185.50	$185.50
7 purchase totals =	$928.40		$1,001.1849	$1,001.19	$1,001.20	$1,001.20