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	$9.50	5.255%	$9.9992	$10.00	$10.00	$10.00
Purchase #2	$217.81	6.359%	$231.6605	$231.66	$231.65	$231.70
Purchase #3	$56.79	9.678%	$62.2861	$62.29	$62.30	$62.30
Purchase #4	$194.32	6.453%	$206.8595	$206.86	$206.85	$206.90
Purchase #5	$37.85	4.335%	$39.4908	$39.49	$39.50	$39.50
Purchase #6	$151.85	13.296%	$172.04	$172.04	$172.05	$172.00
Purchase #7	$245.80	13.867%	$279.8851	$279.89	$279.90	$279.90
7 purchase totals =	$913.92		$1,002.2212	$1,002.23	$1,002.25	$1,002.30