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	$108.71	12.699%	$122.5151	$122.52	$122.50	$122.50
Purchase #2	$112.29	3.715%	$116.4616	$116.46	$116.45	$116.50
Purchase #3	$131.68	8.485%	$142.853	$142.85	$142.85	$142.90
Purchase #4	$48.49	13.629%	$55.0987	$55.10	$55.10	$55.10
Purchase #5	$72.37	5.775%	$76.5494	$76.55	$76.55	$76.50
Purchase #6	$222.30	8.757%	$241.7668	$241.77	$241.75	$241.80
Purchase #7	$133.49	13.321%	$151.2722	$151.27	$151.25	$151.30
7 purchase totals =	$829.33		$906.5168	$906.52	$906.45	$906.60