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	$159.82	13.271%	$181.0297	$181.03	$181.05	$181.00
Purchase #2	$157.27	12.208%	$176.4695	$176.47	$176.45	$176.50
Purchase #3	$13.88	11.813%	$15.5196	$15.52	$15.50	$15.50
Purchase #4	$14.62	11.734%	$16.3355	$16.34	$16.35	$16.30
Purchase #5	$39.55	4.191%	$41.2075	$41.21	$41.20	$41.20
Purchase #6	$27.54	3.807%	$28.5884	$28.59	$28.60	$28.60
Purchase #7	$97.89	13.594%	$111.1972	$111.20	$111.20	$111.20
7 purchase totals =	$510.57		$570.3474	$570.36	$570.35	$570.30