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	$99.42	13.553%	$112.8944	$112.89	$112.90	$112.90
Purchase #2	$36.47	11.579%	$40.6929	$40.69	$40.70	$40.70
Purchase #3	$156.92	10.234%	$172.9792	$172.98	$173.00	$173.00
Purchase #4	$32.27	7.723%	$34.7622	$34.76	$34.75	$34.80
Purchase #5	$61.85	5.439%	$65.214	$65.21	$65.20	$65.20
Purchase #6	$132.87	3.785%	$137.8991	$137.90	$137.90	$137.90
Purchase #7	$66.67	13.836%	$75.8945	$75.89	$75.90	$75.90
7 purchase totals =	$586.47		$640.3363	$640.32	$640.35	$640.40