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	$244.29	4.874%	$256.1967	$256.20	$256.20	$256.20
Purchase #2	$80.32	13.105%	$90.8459	$90.85	$90.85	$90.80
Purchase #3	$179.87	11.214%	$200.0406	$200.04	$200.05	$200.00
Purchase #4	$39.93	13.697%	$45.3992	$45.40	$45.40	$45.40
Purchase #5	$32.45	11.868%	$36.3012	$36.30	$36.30	$36.30
Purchase #6	$105.66	5.412%	$111.3783	$111.38	$111.40	$111.40
Purchase #7	$177.68	7.671%	$191.3098	$191.31	$191.30	$191.30
7 purchase totals =	$860.20		$931.4717	$931.48	$931.50	$931.40