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	$41.93	13.476%	$47.5805	$47.58	$47.60	$47.60
Purchase #2	$128.96	12.509%	$145.0916	$145.09	$145.10	$145.10
Purchase #3	$173.55	4.147%	$180.7471	$180.75	$180.75	$180.70
Purchase #4	$72.52	13.149%	$82.0557	$82.06	$82.05	$82.10
Purchase #5	$129.37	6.246%	$137.4505	$137.45	$137.45	$137.50
Purchase #6	$228.81	7.847%	$246.7647	$246.76	$246.75	$246.80
Purchase #7	$83.51	8.702%	$90.777	$90.78	$90.80	$90.80
7 purchase totals =	$858.65		$930.4671	$930.47	$930.50	$930.60