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	$29.28	11.346%	$32.6021	$32.60	$32.60	$32.60
Purchase #2	$210.64	13.406%	$238.8784	$238.88	$238.90	$238.90
Purchase #3	$81.57	12.131%	$91.4653	$91.47	$91.45	$91.50
Purchase #4	$87.35	4.836%	$91.5742	$91.57	$91.55	$91.60
Purchase #5	$15.73	5.509%	$16.5966	$16.60	$16.60	$16.60
Purchase #6	$225.37	4.545%	$235.6131	$235.61	$235.60	$235.60
Purchase #7	$202.83	10.859%	$224.8553	$224.86	$224.85	$224.90
7 purchase totals =	$852.77		$931.5850	$931.59	$931.55	$931.70