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	$74.40	13.704%	$84.5958	$84.60	$84.60	$84.60
Purchase #2	$104.85	6.244%	$111.3968	$111.40	$111.40	$111.40
Purchase #3	$54.85	7.367%	$58.8908	$58.89	$58.90	$58.90
Purchase #4	$46.72	12.551%	$52.5838	$52.58	$52.60	$52.60
Purchase #5	$81.37	13.616%	$92.4493	$92.45	$92.45	$92.40
Purchase #6	$15.51	10.252%	$17.1001	$17.10	$17.10	$17.10
Purchase #7	$171.58	5.169%	$180.449	$180.45	$180.45	$180.40
7 purchase totals =	$549.28		$597.4656	$597.47	$597.50	$597.40