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	$104.53	3.483%	$108.1708	$108.17	$108.15	$108.20
Purchase #2	$211.57	12.520%	$238.0586	$238.06	$238.05	$238.10
Purchase #3	$123.32	8.743%	$134.1019	$134.10	$134.10	$134.10
Purchase #4	$69.38	13.806%	$78.9586	$78.96	$78.95	$79.00
Purchase #5	$166.58	11.439%	$185.6351	$185.64	$185.65	$185.60
Purchase #6	$191.27	7.286%	$205.2059	$205.21	$205.20	$205.20
Purchase #7	$138.96	5.377%	$146.4319	$146.43	$146.45	$146.40
7 purchase totals =	$1,005.61		$1,096.5628	$1,096.57	$1,096.55	$1,096.60