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	$93.38	7.622%	$100.4974	$100.50	$100.50	$100.50
Purchase #2	$28.64	11.103%	$31.8199	$31.82	$31.80	$31.80
Purchase #3	$12.52	11.716%	$13.9868	$13.99	$14.00	$14.00
Purchase #4	$130.33	10.165%	$143.578	$143.58	$143.60	$143.60
Purchase #5	$154.76	3.378%	$159.9878	$159.99	$160.00	$160.00
Purchase #6	$70.54	3.675%	$73.1323	$73.13	$73.15	$73.10
Purchase #7	$126.98	9.516%	$139.0634	$139.06	$139.05	$139.10
7 purchase totals =	$617.15		$662.0656	$662.07	$662.10	$662.10