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	$152.97	10.669%	$169.2904	$169.29	$169.30	$169.30
Purchase #2	$247.28	3.142%	$255.0495	$255.05	$255.05	$255.00
Purchase #3	$151.61	9.105%	$165.4141	$165.41	$165.40	$165.40
Purchase #4	$128.71	13.533%	$146.1283	$146.13	$146.15	$146.10
Purchase #5	$141.77	12.332%	$159.2531	$159.25	$159.25	$159.30
Purchase #6	$182.85	4.560%	$191.188	$191.19	$191.20	$191.20
Purchase #7	$18.42	8.490%	$19.9839	$19.98	$20.00	$20.00
7 purchase totals =	$1,023.61		$1,106.3073	$1,106.30	$1,106.35	$1,106.30