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	$159.32	12.587%	$179.3736	$179.37	$179.35	$179.40
Purchase #2	$181.42	10.248%	$200.0119	$200.01	$200.00	$200.00
Purchase #3	$114.79	4.464%	$119.9142	$119.91	$119.90	$119.90
Purchase #4	$177.92	5.871%	$188.3657	$188.37	$188.35	$188.40
Purchase #5	$18.87	13.506%	$21.4186	$21.42	$21.40	$21.40
Purchase #6	$74.81	11.756%	$83.6047	$83.60	$83.60	$83.60
Purchase #7	$114.58	10.858%	$127.0211	$127.02	$127.00	$127.00
7 purchase totals =	$841.71		$919.7098	$919.70	$919.60	$919.70