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	$130.50	7.756%	$140.6216	$140.62	$140.60	$140.60
Purchase #2	$79.70	3.503%	$82.4919	$82.49	$82.50	$82.50
Purchase #3	$178.60	8.301%	$193.4256	$193.43	$193.45	$193.40
Purchase #4	$106.40	4.622%	$111.3178	$111.32	$111.30	$111.30
Purchase #5	$154.51	4.503%	$161.4676	$161.47	$161.45	$161.50
Purchase #6	$164.28	8.872%	$178.8549	$178.85	$178.85	$178.90
Purchase #7	$89.95	13.870%	$102.4261	$102.43	$102.45	$102.40
7 purchase totals =	$903.94		$970.6055	$970.61	$970.60	$970.60