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	$8.50	8.466%	$9.2196	$9.22	$9.20	$9.20
Purchase #2	$86.47	7.630%	$93.0677	$93.07	$93.05	$93.10
Purchase #3	$9.54	10.793%	$10.5697	$10.57	$10.55	$10.60
Purchase #4	$59.85	11.184%	$66.5436	$66.54	$66.55	$66.50
Purchase #5	$104.31	7.285%	$111.909	$111.91	$111.90	$111.90
Purchase #6	$147.66	5.708%	$156.0884	$156.09	$156.10	$156.10
Purchase #7	$133.84	8.717%	$145.5068	$145.51	$145.50	$145.50
7 purchase totals =	$550.17		$592.9048	$592.91	$592.85	$592.90