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	$35.43	9.589%	$38.8274	$38.83	$38.85	$38.80
Purchase #2	$123.62	7.312%	$132.6591	$132.66	$132.65	$132.70
Purchase #3	$76.85	11.536%	$85.7154	$85.72	$85.70	$85.70
Purchase #4	$118.95	7.671%	$128.0747	$128.07	$128.05	$128.10
Purchase #5	$12.26	5.233%	$12.9016	$12.90	$12.90	$12.90
Purchase #6	$11.39	9.728%	$12.498	$12.50	$12.50	$12.50
Purchase #7	$58.28	4.299%	$60.7855	$60.79	$60.80	$60.80
7 purchase totals =	$436.78		$471.4617	$471.47	$471.45	$471.50