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	$66.43	12.249%	$74.567	$74.57	$74.55	$74.60
Purchase #2	$89.25	13.587%	$101.3764	$101.38	$101.40	$101.40
Purchase #3	$176.92	5.291%	$186.2808	$186.28	$186.30	$186.30
Purchase #4	$40.59	4.395%	$42.3739	$42.37	$42.35	$42.40
Purchase #5	$103.57	13.365%	$117.4121	$117.41	$117.40	$117.40
Purchase #6	$29.72	12.385%	$33.4008	$33.40	$33.40	$33.40
Purchase #7	$14.83	6.313%	$15.7662	$15.77	$15.75	$15.80
7 purchase totals =	$521.31		$571.1772	$571.18	$571.15	$571.30