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	$250.48	12.421%	$281.5921	$281.59	$281.60	$281.60
Purchase #2	$13.66	10.475%	$15.0909	$15.09	$15.10	$15.10
Purchase #3	$40.87	12.364%	$45.9232	$45.92	$45.90	$45.90
Purchase #4	$5.94	9.542%	$6.5068	$6.51	$6.50	$6.50
Purchase #5	$143.34	12.429%	$161.1557	$161.16	$161.15	$161.20
Purchase #6	$244.57	4.562%	$255.7273	$255.73	$255.75	$255.70
Purchase #7	$212.42	9.165%	$231.8883	$231.89	$231.90	$231.90
7 purchase totals =	$911.28		$997.8843	$997.89	$997.90	$997.90