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	$132.46	6.131%	$140.5811	$140.58	$140.60	$140.60
Purchase #2	$142.64	6.581%	$152.0271	$152.03	$152.05	$152.00
Purchase #3	$127.69	8.385%	$138.3968	$138.40	$138.40	$138.40
Purchase #4	$97.70	7.715%	$105.2376	$105.24	$105.25	$105.20
Purchase #5	$112.47	3.743%	$116.6798	$116.68	$116.70	$116.70
Purchase #6	$102.42	9.251%	$111.8949	$111.89	$111.90	$111.90
Purchase #7	$99.46	5.846%	$105.2744	$105.27	$105.25	$105.30
7 purchase totals =	$814.84		$870.0917	$870.09	$870.15	$870.10