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	$15.91	10.598%	$17.5961	$17.60	$17.60	$17.60
Purchase #2	$95.55	4.206%	$99.5688	$99.57	$99.55	$99.60
Purchase #3	$58.82	12.778%	$66.336	$66.34	$66.35	$66.30
Purchase #4	$233.41	8.705%	$253.7283	$253.73	$253.75	$253.70
Purchase #5	$132.82	6.435%	$141.367	$141.37	$141.35	$141.40
Purchase #6	$98.83	5.679%	$104.4426	$104.44	$104.45	$104.40
Purchase #7	$31.96	10.634%	$35.3586	$35.36	$35.35	$35.40
7 purchase totals =	$667.30		$718.3974	$718.41	$718.40	$718.40