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	$246.63	13.698%	$280.4134	$280.41	$280.40	$280.40
Purchase #2	$199.43	7.825%	$215.0354	$215.04	$215.05	$215.00
Purchase #3	$49.30	12.720%	$55.571	$55.57	$55.55	$55.60
Purchase #4	$34.30	3.417%	$35.472	$35.47	$35.45	$35.50
Purchase #5	$217.76	10.499%	$240.6226	$240.62	$240.60	$240.60
Purchase #6	$37.32	8.734%	$40.5795	$40.58	$40.60	$40.60
Purchase #7	$111.96	13.588%	$127.1731	$127.17	$127.15	$127.20
7 purchase totals =	$896.70		$994.8670	$994.86	$994.80	$994.90