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	$7.88	8.331%	$8.5365	$8.54	$8.55	$8.50
Purchase #2	$167.65	12.497%	$188.6012	$188.60	$188.60	$188.60
Purchase #3	$120.67	13.657%	$137.1499	$137.15	$137.15	$137.10
Purchase #4	$139.69	10.300%	$154.0781	$154.08	$154.10	$154.10
Purchase #5	$198.32	13.853%	$225.7933	$225.79	$225.80	$225.80
Purchase #6	$149.67	10.468%	$165.3375	$165.34	$165.35	$165.30
Purchase #7	$206.69	9.152%	$225.6063	$225.61	$225.60	$225.60
7 purchase totals =	$990.57		$1,105.1028	$1,105.11	$1,105.15	$1,105.00