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	$47.35	7.313%	$50.8127	$50.81	$50.80	$50.80
Purchase #2	$99.44	12.224%	$111.5955	$111.60	$111.60	$111.60
Purchase #3	$142.93	10.589%	$158.0649	$158.06	$158.05	$158.10
Purchase #4	$45.70	10.491%	$50.4944	$50.49	$50.50	$50.50
Purchase #5	$26.43	13.293%	$29.9433	$29.94	$29.95	$29.90
Purchase #6	$39.58	8.321%	$42.8735	$42.87	$42.85	$42.90
Purchase #7	$117.25	13.469%	$133.0424	$133.04	$133.05	$133.00
7 purchase totals =	$518.68		$576.8267	$576.81	$576.80	$576.80