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	$160.54	12.342%	$180.3538	$180.35	$180.35	$180.40
Purchase #2	$216.78	3.832%	$225.087	$225.09	$225.10	$225.10
Purchase #3	$162.72	6.108%	$172.6589	$172.66	$172.65	$172.70
Purchase #4	$103.60	10.184%	$114.1506	$114.15	$114.15	$114.20
Purchase #5	$102.72	8.108%	$111.0485	$111.05	$111.05	$111.00
Purchase #6	$53.78	5.797%	$56.8976	$56.90	$56.90	$56.90
Purchase #7	$106.45	12.636%	$119.901	$119.90	$119.90	$119.90
7 purchase totals =	$906.59		$980.0974	$980.10	$980.10	$980.20