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	$38.45	9.853%	$42.2385	$42.24	$42.25	$42.20
Purchase #2	$236.98	10.610%	$262.1236	$262.12	$262.10	$262.10
Purchase #3	$183.26	3.504%	$189.6814	$189.68	$189.70	$189.70
Purchase #4	$85.30	8.806%	$92.8115	$92.81	$92.80	$92.80
Purchase #5	$78.49	6.586%	$83.6594	$83.66	$83.65	$83.70
Purchase #6	$111.30	11.564%	$124.1707	$124.17	$124.15	$124.20
Purchase #7	$217.53	13.308%	$246.4789	$246.48	$246.50	$246.50
7 purchase totals =	$951.31		$1,041.1640	$1,041.16	$1,041.15	$1,041.20