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	$80.49	11.660%	$89.8751	$89.88	$89.90	$89.90
Purchase #2	$121.68	10.697%	$134.6961	$134.70	$134.70	$134.70
Purchase #3	$52.74	12.615%	$59.3932	$59.39	$59.40	$59.40
Purchase #4	$19.79	4.384%	$20.6576	$20.66	$20.65	$20.70
Purchase #5	$214.53	4.634%	$224.4713	$224.47	$224.45	$224.50
Purchase #6	$17.37	7.643%	$18.6976	$18.70	$18.70	$18.70
Purchase #7	$141.67	8.443%	$153.6312	$153.63	$153.65	$153.60
7 purchase totals =	$648.27		$701.4221	$701.43	$701.45	$701.50