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	$43.28	12.429%	$48.6593	$48.66	$48.65	$48.70
Purchase #2	$185.59	10.621%	$205.3015	$205.30	$205.30	$205.30
Purchase #3	$124.50	3.177%	$128.4554	$128.46	$128.45	$128.50
Purchase #4	$6.85	6.764%	$7.3133	$7.31	$7.30	$7.30
Purchase #5	$18.69	4.211%	$19.477	$19.48	$19.50	$19.50
Purchase #6	$146.48	5.349%	$154.3152	$154.32	$154.30	$154.30
Purchase #7	$9.51	5.624%	$10.0448	$10.04	$10.05	$10.00
7 purchase totals =	$534.90		$573.5665	$573.57	$573.55	$573.60