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	$5.40	3.103%	$5.5676	$5.57	$5.55	$5.60
Purchase #2	$211.91	9.243%	$231.4968	$231.50	$231.50	$231.50
Purchase #3	$16.61	11.797%	$18.5695	$18.57	$18.55	$18.60
Purchase #4	$75.78	4.186%	$78.9522	$78.95	$78.95	$79.00
Purchase #5	$103.85	7.632%	$111.7758	$111.78	$111.80	$111.80
Purchase #6	$157.29	5.349%	$165.7034	$165.70	$165.70	$165.70
Purchase #7	$31.68	10.200%	$34.9114	$34.91	$34.90	$34.90
7 purchase totals =	$602.52		$646.9767	$646.98	$646.95	$647.10