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	$77.69	7.580%	$83.5789	$83.58	$83.60	$83.60
Purchase #2	$130.90	10.142%	$144.1759	$144.18	$144.20	$144.20
Purchase #3	$50.77	8.111%	$54.888	$54.89	$54.90	$54.90
Purchase #4	$153.77	3.535%	$159.2058	$159.21	$159.20	$159.20
Purchase #5	$58.59	4.117%	$61.0022	$61.00	$61.00	$61.00
Purchase #6	$106.57	13.171%	$120.6063	$120.61	$120.60	$120.60
Purchase #7	$226.53	9.388%	$247.7966	$247.80	$247.80	$247.80
7 purchase totals =	$804.82		$871.2537	$871.27	$871.30	$871.30