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	$58.59	13.741%	$66.6409	$66.64	$66.65	$66.60
Purchase #2	$247.32	13.704%	$281.2127	$281.21	$281.20	$281.20
Purchase #3	$139.27	11.222%	$154.8989	$154.90	$154.90	$154.90
Purchase #4	$167.38	7.712%	$180.2883	$180.29	$180.30	$180.30
Purchase #5	$244.93	4.485%	$255.9151	$255.92	$255.90	$255.90
Purchase #6	$108.38	8.235%	$117.3051	$117.31	$117.30	$117.30
Purchase #7	$51.69	9.540%	$56.6212	$56.62	$56.60	$56.60
7 purchase totals =	$1,017.56		$1,112.8822	$1,112.89	$1,112.85	$1,112.80