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	$15.51	7.157%	$16.6201	$16.62	$16.60	$16.60
Purchase #2	$215.31	5.649%	$227.4729	$227.47	$227.45	$227.50
Purchase #3	$178.59	6.545%	$190.2787	$190.28	$190.30	$190.30
Purchase #4	$184.82	8.720%	$200.9363	$200.94	$200.95	$200.90
Purchase #5	$62.36	7.826%	$67.2403	$67.24	$67.25	$67.20
Purchase #6	$91.60	4.661%	$95.8695	$95.87	$95.85	$95.90
Purchase #7	$169.77	10.458%	$187.5245	$187.52	$187.50	$187.50
7 purchase totals =	$917.96		$985.9423	$985.94	$985.90	$985.90