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	$57.91	10.327%	$63.8904	$63.89	$63.90	$63.90
Purchase #2	$75.86	12.422%	$85.2833	$85.28	$85.30	$85.30
Purchase #3	$55.70	7.560%	$59.9109	$59.91	$59.90	$59.90
Purchase #4	$38.60	5.846%	$40.8566	$40.86	$40.85	$40.90
Purchase #5	$73.80	9.378%	$80.721	$80.72	$80.70	$80.70
Purchase #6	$132.95	4.145%	$138.4608	$138.46	$138.45	$138.50
Purchase #7	$192.30	11.466%	$214.3491	$214.35	$214.35	$214.30
7 purchase totals =	$627.12		$683.4721	$683.47	$683.45	$683.50