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	$66.30	4.345%	$69.1807	$69.18	$69.20	$69.20
Purchase #2	$43.57	5.248%	$45.8566	$45.86	$45.85	$45.90
Purchase #3	$236.34	4.126%	$246.0914	$246.09	$246.10	$246.10
Purchase #4	$33.92	11.207%	$37.7214	$37.72	$37.70	$37.70
Purchase #5	$156.48	11.123%	$173.8853	$173.89	$173.90	$173.90
Purchase #6	$137.47	13.136%	$155.5281	$155.53	$155.55	$155.50
Purchase #7	$87.51	8.862%	$95.2651	$95.27	$95.25	$95.30
7 purchase totals =	$761.59		$823.5286	$823.54	$823.55	$823.60