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	$95.90	8.224%	$103.7868	$103.79	$103.80	$103.80
Purchase #2	$169.97	7.619%	$182.92	$182.92	$182.90	$182.90
Purchase #3	$18.66	4.676%	$19.5325	$19.53	$19.55	$19.50
Purchase #4	$216.55	5.616%	$228.7114	$228.71	$228.70	$228.70
Purchase #5	$210.87	3.325%	$217.8814	$217.88	$217.90	$217.90
Purchase #6	$103.50	7.580%	$111.3453	$111.35	$111.35	$111.30
Purchase #7	$97.59	6.414%	$103.8494	$103.85	$103.85	$103.80
7 purchase totals =	$913.04		$968.0268	$968.03	$968.05	$967.90