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	$248.95	12.211%	$279.3493	$279.35	$279.35	$279.30
Purchase #2	$219.72	7.615%	$236.4517	$236.45	$236.45	$236.50
Purchase #3	$231.93	10.331%	$255.8907	$255.89	$255.90	$255.90
Purchase #4	$21.95	11.671%	$24.5118	$24.51	$24.50	$24.50
Purchase #5	$92.67	7.684%	$99.7908	$99.79	$99.80	$99.80
Purchase #6	$132.30	8.139%	$143.0679	$143.07	$143.05	$143.10
Purchase #7	$45.85	7.252%	$49.175	$49.18	$49.20	$49.20
7 purchase totals =	$993.37		$1,088.2372	$1,088.24	$1,088.25	$1,088.30