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	$99.62	12.150%	$111.7238	$111.72	$111.70	$111.70
Purchase #2	$115.89	13.110%	$131.0832	$131.08	$131.10	$131.10
Purchase #3	$206.72	10.103%	$227.6049	$227.60	$227.60	$227.60
Purchase #4	$227.39	6.465%	$242.0908	$242.09	$242.10	$242.10
Purchase #5	$62.49	6.589%	$66.6075	$66.61	$66.60	$66.60
Purchase #6	$31.67	11.214%	$35.2215	$35.22	$35.20	$35.20
Purchase #7	$95.61	10.291%	$105.4492	$105.45	$105.45	$105.40
7 purchase totals =	$839.39		$919.7809	$919.77	$919.75	$919.70