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	$42.45	12.140%	$47.6034	$47.60	$47.60	$47.60
Purchase #2	$103.89	8.307%	$112.5201	$112.52	$112.50	$112.50
Purchase #3	$203.58	6.617%	$217.0509	$217.05	$217.05	$217.10
Purchase #4	$108.79	13.807%	$123.8106	$123.81	$123.80	$123.80
Purchase #5	$43.73	9.375%	$47.8297	$47.83	$47.85	$47.80
Purchase #6	$14.27	6.370%	$15.179	$15.18	$15.20	$15.20
Purchase #7	$111.82	6.776%	$119.3969	$119.40	$119.40	$119.40
7 purchase totals =	$628.53		$683.3906	$683.39	$683.40	$683.40