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	$223.34	12.674%	$251.6461	$251.65	$251.65	$251.60
Purchase #2	$128.51	12.406%	$144.453	$144.45	$144.45	$144.50
Purchase #3	$157.30	9.852%	$172.7972	$172.80	$172.80	$172.80
Purchase #4	$30.88	12.443%	$34.7224	$34.72	$34.70	$34.70
Purchase #5	$93.54	11.321%	$104.1297	$104.13	$104.15	$104.10
Purchase #6	$137.98	7.603%	$148.4706	$148.47	$148.45	$148.50
Purchase #7	$71.91	11.701%	$80.3242	$80.32	$80.30	$80.30
7 purchase totals =	$843.46		$936.5432	$936.54	$936.50	$936.50