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	$155.82	6.397%	$165.7878	$165.79	$165.80	$165.80
Purchase #2	$45.92	6.597%	$48.9493	$48.95	$48.95	$48.90
Purchase #3	$245.72	12.135%	$275.5381	$275.54	$275.55	$275.50
Purchase #4	$233.40	5.261%	$245.6792	$245.68	$245.70	$245.70
Purchase #5	$196.87	7.254%	$211.1509	$211.15	$211.15	$211.20
Purchase #6	$244.66	4.341%	$255.2807	$255.28	$255.30	$255.30
Purchase #7	$243.63	12.389%	$273.8133	$273.81	$273.80	$273.80
7 purchase totals =	$1,366.02		$1,476.1993	$1,476.20	$1,476.25	$1,476.20