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	$69.63	13.120%	$78.7655	$78.77	$78.75	$78.80
Purchase #2	$231.81	11.193%	$257.7565	$257.76	$257.75	$257.80
Purchase #3	$109.96	12.375%	$123.5676	$123.57	$123.55	$123.60
Purchase #4	$100.68	10.490%	$111.2413	$111.24	$111.25	$111.20
Purchase #5	$8.86	7.576%	$9.5312	$9.53	$9.55	$9.50
Purchase #6	$34.94	7.568%	$37.5843	$37.58	$37.60	$37.60
Purchase #7	$61.95	7.381%	$66.5225	$66.52	$66.50	$66.50
7 purchase totals =	$617.83		$684.9689	$684.97	$684.95	$685.00