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	$244.87	4.742%	$256.4817	$256.48	$256.50	$256.50
Purchase #2	$126.87	13.186%	$143.5991	$143.60	$143.60	$143.60
Purchase #3	$46.30	9.784%	$50.83	$50.83	$50.85	$50.80
Purchase #4	$18.88	12.569%	$21.253	$21.25	$21.25	$21.30
Purchase #5	$142.60	12.538%	$160.4792	$160.48	$160.50	$160.50
Purchase #6	$38.93	4.158%	$40.5487	$40.55	$40.55	$40.50
Purchase #7	$146.78	10.846%	$162.6998	$162.70	$162.70	$162.70
7 purchase totals =	$765.23		$835.8915	$835.89	$835.95	$835.90