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	$248.63	3.590%	$257.5558	$257.56	$257.55	$257.60
Purchase #2	$127.33	5.478%	$134.3051	$134.31	$134.30	$134.30
Purchase #3	$106.32	12.247%	$119.341	$119.34	$119.35	$119.30
Purchase #4	$57.61	10.426%	$63.6164	$63.62	$63.60	$63.60
Purchase #5	$53.32	5.833%	$56.4302	$56.43	$56.45	$56.40
Purchase #6	$43.72	10.343%	$48.242	$48.24	$48.25	$48.20
Purchase #7	$170.90	11.520%	$190.5877	$190.59	$190.60	$190.60
7 purchase totals =	$807.83		$870.0782	$870.09	$870.10	$870.00