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	$144.35	10.499%	$159.5053	$159.51	$159.50	$159.50
Purchase #2	$61.61	5.753%	$65.1544	$65.15	$65.15	$65.20
Purchase #3	$95.49	6.717%	$101.9041	$101.90	$101.90	$101.90
Purchase #4	$38.80	13.759%	$44.1385	$44.14	$44.15	$44.10
Purchase #5	$46.48	8.638%	$50.4949	$50.49	$50.50	$50.50
Purchase #6	$10.52	11.119%	$11.6897	$11.69	$11.70	$11.70
Purchase #7	$67.52	5.342%	$71.1269	$71.13	$71.15	$71.10
7 purchase totals =	$464.77		$504.0138	$504.01	$504.05	$504.00