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	$31.90	9.477%	$34.9232	$34.92	$34.90	$34.90
Purchase #2	$207.37	9.822%	$227.7379	$227.74	$227.75	$227.70
Purchase #3	$53.67	10.126%	$59.1046	$59.10	$59.10	$59.10
Purchase #4	$218.62	11.237%	$243.1863	$243.19	$243.20	$243.20
Purchase #5	$51.94	4.867%	$54.4679	$54.47	$54.45	$54.50
Purchase #6	$39.99	13.641%	$45.445	$45.45	$45.45	$45.40
Purchase #7	$204.42	10.379%	$225.6368	$225.64	$225.65	$225.60
7 purchase totals =	$807.91		$890.5017	$890.51	$890.50	$890.40