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	$83.47	6.724%	$89.0825	$89.08	$89.10	$89.10
Purchase #2	$16.78	8.148%	$18.1472	$18.15	$18.15	$18.10
Purchase #3	$138.49	9.536%	$151.6964	$151.70	$151.70	$151.70
Purchase #4	$23.54	4.210%	$24.531	$24.53	$24.55	$24.50
Purchase #5	$221.32	5.296%	$233.0411	$233.04	$233.05	$233.00
Purchase #6	$12.49	12.849%	$14.0948	$14.09	$14.10	$14.10
Purchase #7	$55.87	10.772%	$61.8883	$61.89	$61.90	$61.90
7 purchase totals =	$551.96		$592.4813	$592.48	$592.55	$592.40