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	$94.38	6.427%	$100.4458	$100.45	$100.45	$100.40
Purchase #2	$190.88	12.162%	$214.0948	$214.09	$214.10	$214.10
Purchase #3	$98.32	13.383%	$111.4782	$111.48	$111.50	$111.50
Purchase #4	$74.95	3.420%	$77.5133	$77.51	$77.50	$77.50
Purchase #5	$30.58	6.197%	$32.475	$32.48	$32.50	$32.50
Purchase #6	$244.45	5.456%	$257.7872	$257.79	$257.80	$257.80
Purchase #7	$23.54	6.492%	$25.0682	$25.07	$25.05	$25.10
7 purchase totals =	$757.10		$818.8625	$818.87	$818.90	$818.90