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	$35.41	11.396%	$39.4453	$39.45	$39.45	$39.40
Purchase #2	$174.80	9.161%	$190.8134	$190.81	$190.80	$190.80
Purchase #3	$134.57	3.338%	$139.0619	$139.06	$139.05	$139.10
Purchase #4	$40.78	3.376%	$42.1567	$42.16	$42.15	$42.20
Purchase #5	$92.68	11.157%	$103.0203	$103.02	$103.00	$103.00
Purchase #6	$51.53	6.378%	$54.8166	$54.82	$54.80	$54.80
Purchase #7	$166.47	13.861%	$189.5444	$189.54	$189.55	$189.50
7 purchase totals =	$696.24		$758.8586	$758.86	$758.80	$758.80