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	$139.64	11.549%	$155.767	$155.77	$155.75	$155.80
Purchase #2	$96.96	12.186%	$108.7755	$108.78	$108.80	$108.80
Purchase #3	$160.59	12.393%	$180.4919	$180.49	$180.50	$180.50
Purchase #4	$217.85	11.350%	$242.576	$242.58	$242.60	$242.60
Purchase #5	$35.67	7.740%	$38.4309	$38.43	$38.45	$38.40
Purchase #6	$222.34	8.419%	$241.0588	$241.06	$241.05	$241.10
Purchase #7	$146.67	12.728%	$165.3382	$165.34	$165.35	$165.30
7 purchase totals =	$1,019.72		$1,132.4383	$1,132.45	$1,132.50	$1,132.50