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	$11.42	12.492%	$12.8466	$12.85	$12.85	$12.80
Purchase #2	$58.51	13.445%	$66.3767	$66.38	$66.40	$66.40
Purchase #3	$139.30	10.369%	$153.744	$153.74	$153.75	$153.70
Purchase #4	$61.28	3.485%	$63.4156	$63.42	$63.40	$63.40
Purchase #5	$45.42	13.690%	$51.638	$51.64	$51.65	$51.60
Purchase #6	$151.65	13.731%	$172.4731	$172.47	$172.45	$172.50
Purchase #7	$30.35	6.175%	$32.2241	$32.22	$32.20	$32.20
7 purchase totals =	$497.93		$552.7181	$552.72	$552.70	$552.60