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	$50.89	11.357%	$56.6696	$56.67	$56.65	$56.70
Purchase #2	$54.76	8.547%	$59.4403	$59.44	$59.45	$59.40
Purchase #3	$62.73	6.412%	$66.7522	$66.75	$66.75	$66.80
Purchase #4	$27.27	8.189%	$29.5031	$29.50	$29.50	$29.50
Purchase #5	$142.52	3.757%	$147.8745	$147.87	$147.85	$147.90
Purchase #6	$126.85	6.184%	$134.6944	$134.69	$134.70	$134.70
Purchase #7	$86.75	4.591%	$90.7327	$90.73	$90.75	$90.70
7 purchase totals =	$551.77		$585.6668	$585.65	$585.65	$585.70