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	$126.62	13.382%	$143.5643	$143.56	$143.55	$143.60
Purchase #2	$40.66	11.102%	$45.1741	$45.17	$45.15	$45.20
Purchase #3	$238.85	7.559%	$256.9047	$256.90	$256.90	$256.90
Purchase #4	$46.62	4.385%	$48.6643	$48.66	$48.65	$48.70
Purchase #5	$128.34	11.749%	$143.4187	$143.42	$143.40	$143.40
Purchase #6	$70.53	10.406%	$77.8694	$77.87	$77.85	$77.90
Purchase #7	$140.85	11.572%	$157.1492	$157.15	$157.15	$157.10
7 purchase totals =	$792.47		$872.7447	$872.73	$872.65	$872.80