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	$8.39	11.677%	$9.3697	$9.37	$9.35	$9.40
Purchase #2	$102.26	5.619%	$108.006	$108.01	$108.00	$108.00
Purchase #3	$95.37	10.358%	$105.2484	$105.25	$105.25	$105.20
Purchase #4	$71.42	6.727%	$76.2244	$76.22	$76.20	$76.20
Purchase #5	$122.58	4.789%	$128.4504	$128.45	$128.45	$128.50
Purchase #6	$64.36	13.197%	$72.8536	$72.85	$72.85	$72.90
Purchase #7	$106.66	4.490%	$111.449	$111.45	$111.45	$111.40
7 purchase totals =	$571.04		$611.6015	$611.60	$611.55	$611.60