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	$39.49	7.286%	$42.3672	$42.37	$42.35	$42.40
Purchase #2	$172.91	8.421%	$187.4708	$187.47	$187.45	$187.50
Purchase #3	$242.89	5.494%	$256.2344	$256.23	$256.25	$256.20
Purchase #4	$137.55	6.768%	$146.8594	$146.86	$146.85	$146.90
Purchase #5	$130.74	13.559%	$148.467	$148.47	$148.45	$148.50
Purchase #6	$42.80	8.671%	$46.5112	$46.51	$46.50	$46.50
Purchase #7	$116.52	11.200%	$129.5702	$129.57	$129.55	$129.60
7 purchase totals =	$882.90		$957.4802	$957.48	$957.40	$957.60