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	$52.75	11.693%	$58.9181	$58.92	$58.90	$58.90
Purchase #2	$105.83	5.288%	$111.4263	$111.43	$111.45	$111.40
Purchase #3	$42.57	5.647%	$44.9739	$44.97	$44.95	$45.00
Purchase #4	$95.53	12.516%	$107.4865	$107.49	$107.50	$107.50
Purchase #5	$100.97	10.824%	$111.899	$111.90	$111.90	$111.90
Purchase #6	$118.60	13.213%	$134.2706	$134.27	$134.25	$134.30
Purchase #7	$139.61	9.403%	$152.7375	$152.74	$152.75	$152.70
7 purchase totals =	$655.86		$721.7119	$721.72	$721.70	$721.70