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	$82.82	5.763%	$87.5929	$87.59	$87.60	$87.60
Purchase #2	$63.49	5.385%	$66.9089	$66.91	$66.90	$66.90
Purchase #3	$42.40	10.295%	$46.7651	$46.77	$46.75	$46.80
Purchase #4	$11.31	6.266%	$12.0187	$12.02	$12.00	$12.00
Purchase #5	$223.65	8.277%	$242.1615	$242.16	$242.15	$242.20
Purchase #6	$100.82	10.612%	$111.519	$111.52	$111.50	$111.50
Purchase #7	$12.42	12.342%	$13.9529	$13.95	$13.95	$14.00
7 purchase totals =	$536.91		$580.9190	$580.92	$580.85	$581.00