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	$25.90	13.790%	$29.4716	$29.47	$29.45	$29.50
Purchase #2	$78.52	3.212%	$81.0421	$81.04	$81.05	$81.00
Purchase #3	$100.38	11.426%	$111.8494	$111.85	$111.85	$111.80
Purchase #4	$24.77	3.221%	$25.5678	$25.57	$25.55	$25.60
Purchase #5	$171.89	13.720%	$195.4733	$195.47	$195.45	$195.50
Purchase #6	$25.75	10.290%	$28.3997	$28.40	$28.40	$28.40
Purchase #7	$237.31	7.714%	$255.6161	$255.62	$255.60	$255.60
7 purchase totals =	$664.52		$727.4200	$727.42	$727.35	$727.40