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	$133.70	12.545%	$150.4727	$150.47	$150.45	$150.50
Purchase #2	$131.79	10.390%	$145.483	$145.48	$145.50	$145.50
Purchase #3	$158.87	11.653%	$177.3831	$177.38	$177.40	$177.40
Purchase #4	$196.55	13.129%	$222.355	$222.36	$222.35	$222.40
Purchase #5	$141.48	6.139%	$150.1655	$150.17	$150.15	$150.20
Purchase #6	$73.42	10.447%	$81.0902	$81.09	$81.10	$81.10
Purchase #7	$59.42	10.463%	$65.6371	$65.64	$65.65	$65.60
7 purchase totals =	$895.23		$992.5866	$992.59	$992.60	$992.70