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	$235.49	8.789%	$256.1872	$256.19	$256.20	$256.20
Purchase #2	$59.57	11.761%	$66.576	$66.58	$66.60	$66.60
Purchase #3	$8.97	11.107%	$9.9663	$9.97	$9.95	$10.00
Purchase #4	$243.88	4.616%	$255.1375	$255.14	$255.15	$255.10
Purchase #5	$90.74	11.184%	$100.8884	$100.89	$100.90	$100.90
Purchase #6	$83.61	10.579%	$92.4551	$92.46	$92.45	$92.50
Purchase #7	$30.25	12.543%	$34.0443	$34.04	$34.05	$34.00
7 purchase totals =	$752.51		$815.2548	$815.27	$815.30	$815.30