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	$65.48	4.230%	$68.2498	$68.25	$68.25	$68.20
Purchase #2	$35.64	10.767%	$39.4774	$39.48	$39.50	$39.50
Purchase #3	$38.96	3.778%	$40.4319	$40.43	$40.45	$40.40
Purchase #4	$123.71	12.655%	$139.3655	$139.37	$139.35	$139.40
Purchase #5	$112.57	13.791%	$128.0945	$128.09	$128.10	$128.10
Purchase #6	$95.85	12.639%	$107.9645	$107.96	$107.95	$108.00
Purchase #7	$54.94	7.521%	$59.072	$59.07	$59.05	$59.10
7 purchase totals =	$527.15		$582.6556	$582.65	$582.65	$582.70