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	$123.68	10.177%	$136.2669	$136.27	$136.25	$136.30
Purchase #2	$139.53	10.262%	$153.8486	$153.85	$153.85	$153.80
Purchase #3	$116.81	12.284%	$131.1589	$131.16	$131.15	$131.20
Purchase #4	$37.55	8.441%	$40.7196	$40.72	$40.70	$40.70
Purchase #5	$113.67	12.390%	$127.7537	$127.75	$127.75	$127.80
Purchase #6	$89.81	11.348%	$100.0016	$100.00	$100.00	$100.00
Purchase #7	$114.62	5.438%	$120.853	$120.85	$120.85	$120.90
7 purchase totals =	$735.67		$810.6023	$810.60	$810.55	$810.70