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	$51.72	13.738%	$58.8253	$58.83	$58.85	$58.80
Purchase #2	$21.74	6.305%	$23.1107	$23.11	$23.10	$23.10
Purchase #3	$234.40	12.423%	$263.5195	$263.52	$263.50	$263.50
Purchase #4	$145.61	4.168%	$151.679	$151.68	$151.70	$151.70
Purchase #5	$223.48	7.757%	$240.8153	$240.82	$240.80	$240.80
Purchase #6	$100.96	10.810%	$111.8738	$111.87	$111.85	$111.90
Purchase #7	$171.51	5.103%	$180.2622	$180.26	$180.25	$180.30
7 purchase totals =	$949.42		$1,030.0858	$1,030.09	$1,030.05	$1,030.10