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	$7.92	6.575%	$8.4407	$8.44	$8.45	$8.40
Purchase #2	$13.43	4.744%	$14.0671	$14.07	$14.05	$14.10
Purchase #3	$246.89	13.655%	$280.6028	$280.60	$280.60	$280.60
Purchase #4	$93.98	9.349%	$102.7662	$102.77	$102.75	$102.80
Purchase #5	$100.27	10.815%	$111.1142	$111.11	$111.10	$111.10
Purchase #6	$147.70	7.266%	$158.4319	$158.43	$158.45	$158.40
Purchase #7	$6.58	7.766%	$7.091	$7.09	$7.10	$7.10
7 purchase totals =	$616.77		$682.5139	$682.51	$682.50	$682.50