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	$140.71	12.725%	$158.6153	$158.62	$158.60	$158.60
Purchase #2	$169.33	10.300%	$186.771	$186.77	$186.75	$186.80
Purchase #3	$102.30	11.510%	$114.0747	$114.07	$114.05	$114.10
Purchase #4	$40.49	13.332%	$45.8881	$45.89	$45.90	$45.90
Purchase #5	$45.75	5.238%	$48.1464	$48.15	$48.15	$48.10
Purchase #6	$213.45	13.153%	$241.5251	$241.53	$241.55	$241.50
Purchase #7	$51.79	11.228%	$57.605	$57.61	$57.60	$57.60
7 purchase totals =	$763.82		$852.6256	$852.64	$852.60	$852.60