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	$112.52	13.313%	$127.4998	$127.50	$127.50	$127.50
Purchase #2	$146.35	13.452%	$166.037	$166.04	$166.05	$166.00
Purchase #3	$137.60	13.497%	$156.1719	$156.17	$156.15	$156.20
Purchase #4	$144.60	7.769%	$155.834	$155.83	$155.85	$155.80
Purchase #5	$27.89	6.841%	$29.798	$29.80	$29.80	$29.80
Purchase #6	$62.76	12.215%	$70.4261	$70.43	$70.45	$70.40
Purchase #7	$52.25	4.687%	$54.699	$54.70	$54.70	$54.70
7 purchase totals =	$683.97		$760.4658	$760.47	$760.50	$760.40