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	$183.68	13.564%	$208.5944	$208.59	$208.60	$208.60
Purchase #2	$90.88	10.831%	$100.7232	$100.72	$100.70	$100.70
Purchase #3	$129.43	7.507%	$139.1463	$139.15	$139.15	$139.10
Purchase #4	$112.50	9.486%	$123.1718	$123.17	$123.15	$123.20
Purchase #5	$148.42	7.729%	$159.8914	$159.89	$159.90	$159.90
Purchase #6	$28.77	4.633%	$30.1029	$30.10	$30.10	$30.10
Purchase #7	$71.63	6.715%	$76.44	$76.44	$76.45	$76.40
7 purchase totals =	$765.31		$838.0700	$838.06	$838.05	$838.00