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	$202.92	9.707%	$222.6174	$222.62	$222.60	$222.60
Purchase #2	$35.42	3.514%	$36.6647	$36.66	$36.65	$36.70
Purchase #3	$31.61	9.567%	$34.6341	$34.63	$34.65	$34.60
Purchase #4	$105.55	10.380%	$116.5061	$116.51	$116.50	$116.50
Purchase #5	$66.70	3.277%	$68.8858	$68.89	$68.90	$68.90
Purchase #6	$33.69	10.613%	$37.2655	$37.27	$37.25	$37.30
Purchase #7	$131.67	5.552%	$138.9803	$138.98	$139.00	$139.00
7 purchase totals =	$607.56		$655.5539	$655.56	$655.55	$655.60