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	$55.97	9.307%	$61.1791	$61.18	$61.20	$61.20
Purchase #2	$70.34	8.772%	$76.5102	$76.51	$76.50	$76.50
Purchase #3	$131.43	9.204%	$143.5268	$143.53	$143.55	$143.50
Purchase #4	$68.89	10.845%	$76.3611	$76.36	$76.35	$76.40
Purchase #5	$168.89	13.129%	$191.0636	$191.06	$191.05	$191.10
Purchase #6	$245.30	9.756%	$269.2315	$269.23	$269.25	$269.20
Purchase #7	$155.93	11.333%	$173.6015	$173.60	$173.60	$173.60
7 purchase totals =	$896.75		$991.4738	$991.47	$991.50	$991.50