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	$69.85	13.469%	$79.2581	$79.26	$79.25	$79.30
Purchase #2	$108.46	3.160%	$111.8873	$111.89	$111.90	$111.90
Purchase #3	$181.43	5.469%	$191.3524	$191.35	$191.35	$191.40
Purchase #4	$14.46	6.697%	$15.4284	$15.43	$15.45	$15.40
Purchase #5	$131.89	8.790%	$143.4831	$143.48	$143.50	$143.50
Purchase #6	$16.35	5.594%	$17.2646	$17.26	$17.25	$17.30
Purchase #7	$123.42	7.325%	$132.4605	$132.46	$132.45	$132.50
7 purchase totals =	$645.86		$691.1344	$691.13	$691.15	$691.30