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	$207.60	13.225%	$235.0551	$235.06	$235.05	$235.10
Purchase #2	$137.66	13.679%	$156.4905	$156.49	$156.50	$156.50
Purchase #3	$224.96	6.208%	$238.9255	$238.93	$238.95	$238.90
Purchase #4	$92.52	6.700%	$98.7188	$98.72	$98.70	$98.70
Purchase #5	$132.29	7.105%	$141.6892	$141.69	$141.70	$141.70
Purchase #6	$18.35	8.756%	$19.9567	$19.96	$19.95	$20.00
Purchase #7	$107.52	4.785%	$112.6648	$112.66	$112.65	$112.70
7 purchase totals =	$920.90		$1,003.5006	$1,003.51	$1,003.50	$1,003.60