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	$104.32	6.797%	$111.4106	$111.41	$111.40	$111.40
Purchase #2	$76.31	12.500%	$85.8488	$85.85	$85.85	$85.80
Purchase #3	$161.75	10.204%	$178.255	$178.26	$178.25	$178.30
Purchase #4	$50.40	4.153%	$52.4931	$52.49	$52.50	$52.50
Purchase #5	$14.82	5.129%	$15.5801	$15.58	$15.60	$15.60
Purchase #6	$208.72	9.184%	$227.8888	$227.89	$227.90	$227.90
Purchase #7	$33.41	13.737%	$37.9995	$38.00	$38.00	$38.00
7 purchase totals =	$649.73		$709.4759	$709.48	$709.50	$709.50