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	$225.81	13.532%	$256.3666	$256.37	$256.35	$256.40
Purchase #2	$86.57	5.554%	$91.3781	$91.38	$91.40	$91.40
Purchase #3	$27.45	6.553%	$29.2488	$29.25	$29.25	$29.20
Purchase #4	$58.45	8.792%	$63.5889	$63.59	$63.60	$63.60
Purchase #5	$92.48	8.481%	$100.3232	$100.32	$100.30	$100.30
Purchase #6	$18.95	11.567%	$21.1419	$21.14	$21.15	$21.10
Purchase #7	$158.85	12.388%	$178.5283	$178.53	$178.55	$178.50
7 purchase totals =	$668.56		$740.5758	$740.58	$740.60	$740.50