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	$167.35	13.488%	$189.9222	$189.92	$189.90	$189.90
Purchase #2	$114.38	9.233%	$124.9407	$124.94	$124.95	$124.90
Purchase #3	$132.62	8.491%	$143.8808	$143.88	$143.90	$143.90
Purchase #4	$9.52	6.719%	$10.1596	$10.16	$10.15	$10.20
Purchase #5	$71.85	9.387%	$78.5946	$78.59	$78.60	$78.60
Purchase #6	$32.64	9.356%	$35.6938	$35.69	$35.70	$35.70
Purchase #7	$83.61	7.682%	$90.0329	$90.03	$90.05	$90.00
7 purchase totals =	$611.97		$673.2246	$673.21	$673.25	$673.20