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	$53.86	3.770%	$55.8905	$55.89	$55.90	$55.90
Purchase #2	$112.93	9.630%	$123.8052	$123.81	$123.80	$123.80
Purchase #3	$128.63	11.652%	$143.618	$143.62	$143.60	$143.60
Purchase #4	$159.43	4.169%	$166.0766	$166.08	$166.10	$166.10
Purchase #5	$13.88	11.490%	$15.4748	$15.47	$15.45	$15.50
Purchase #6	$231.63	10.689%	$256.3889	$256.39	$256.40	$256.40
Purchase #7	$153.98	4.285%	$160.578	$160.58	$160.60	$160.60
7 purchase totals =	$854.34		$921.8320	$921.84	$921.85	$921.90