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	$108.34	7.619%	$116.5944	$116.59	$116.60	$116.60
Purchase #2	$100.34	11.223%	$111.6012	$111.60	$111.60	$111.60
Purchase #3	$192.48	3.728%	$199.6557	$199.66	$199.65	$199.70
Purchase #4	$195.60	5.690%	$206.7296	$206.73	$206.75	$206.70
Purchase #5	$12.90	11.485%	$14.3816	$14.38	$14.40	$14.40
Purchase #6	$139.52	13.197%	$157.9325	$157.93	$157.95	$157.90
Purchase #7	$29.87	5.409%	$31.4857	$31.49	$31.50	$31.50
7 purchase totals =	$779.05		$838.3807	$838.38	$838.45	$838.40