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	$122.65	12.169%	$137.5753	$137.58	$137.60	$137.60
Purchase #2	$208.57	10.394%	$230.2488	$230.25	$230.25	$230.20
Purchase #3	$82.29	3.486%	$85.1586	$85.16	$85.15	$85.20
Purchase #4	$55.50	6.790%	$59.2685	$59.27	$59.25	$59.30
Purchase #5	$125.71	12.171%	$141.0102	$141.01	$141.00	$141.00
Purchase #6	$82.93	13.347%	$93.9987	$94.00	$94.00	$94.00
Purchase #7	$109.83	11.851%	$122.846	$122.85	$122.85	$122.80
7 purchase totals =	$787.48		$870.1061	$870.12	$870.10	$870.10