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	$134.33	10.841%	$148.8927	$148.89	$148.90	$148.90
Purchase #2	$186.27	7.281%	$199.8323	$199.83	$199.85	$199.80
Purchase #3	$40.50	4.748%	$42.4229	$42.42	$42.40	$42.40
Purchase #4	$155.29	10.853%	$172.1436	$172.14	$172.15	$172.10
Purchase #5	$71.30	8.720%	$77.5174	$77.52	$77.50	$77.50
Purchase #6	$61.86	13.222%	$70.0391	$70.04	$70.05	$70.00
Purchase #7	$99.74	5.622%	$105.3474	$105.35	$105.35	$105.30
7 purchase totals =	$749.29		$816.1954	$816.19	$816.20	$816.00