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	$59.42	3.189%	$61.3149	$61.31	$61.30	$61.30
Purchase #2	$77.50	4.792%	$81.2138	$81.21	$81.20	$81.20
Purchase #3	$160.53	7.692%	$172.878	$172.88	$172.90	$172.90
Purchase #4	$13.29	12.420%	$14.9406	$14.94	$14.95	$14.90
Purchase #5	$162.48	4.509%	$169.8062	$169.81	$169.80	$169.80
Purchase #6	$82.60	6.553%	$88.0128	$88.01	$88.00	$88.00
Purchase #7	$209.83	5.715%	$221.8218	$221.82	$221.80	$221.80
7 purchase totals =	$765.65		$809.9881	$809.98	$809.95	$809.90