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	$75.38	13.416%	$85.493	$85.49	$85.50	$85.50
Purchase #2	$141.69	11.475%	$157.9489	$157.95	$157.95	$157.90
Purchase #3	$57.83	13.267%	$65.5023	$65.50	$65.50	$65.50
Purchase #4	$61.74	8.366%	$66.9052	$66.91	$66.90	$66.90
Purchase #5	$231.79	11.357%	$258.1144	$258.11	$258.10	$258.10
Purchase #6	$87.41	3.643%	$90.5943	$90.59	$90.60	$90.60
Purchase #7	$34.77	6.818%	$37.1406	$37.14	$37.15	$37.10
7 purchase totals =	$690.61		$761.6987	$761.69	$761.70	$761.60