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	$229.48	11.653%	$256.2213	$256.22	$256.20	$256.20
Purchase #2	$105.83	10.737%	$117.193	$117.19	$117.20	$117.20
Purchase #3	$144.28	7.624%	$155.2799	$155.28	$155.30	$155.30
Purchase #4	$138.27	11.746%	$154.5112	$154.51	$154.50	$154.50
Purchase #5	$86.64	10.196%	$95.4738	$95.47	$95.45	$95.50
Purchase #6	$18.59	10.416%	$20.5263	$20.53	$20.55	$20.50
Purchase #7	$247.65	11.165%	$275.3001	$275.30	$275.30	$275.30
7 purchase totals =	$970.74		$1,074.5056	$1,074.50	$1,074.50	$1,074.50