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	$48.60	11.367%	$54.1244	$54.12	$54.10	$54.10
Purchase #2	$189.68	3.767%	$196.8252	$196.83	$196.85	$196.80
Purchase #3	$57.60	4.214%	$60.0273	$60.03	$60.05	$60.00
Purchase #4	$29.30	9.750%	$32.1568	$32.16	$32.15	$32.20
Purchase #5	$148.82	6.422%	$158.3772	$158.38	$158.40	$158.40
Purchase #6	$83.25	4.522%	$87.0146	$87.01	$87.00	$87.00
Purchase #7	$247.87	9.660%	$271.8142	$271.81	$271.80	$271.80
7 purchase totals =	$805.12		$860.3397	$860.34	$860.35	$860.30