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	$128.38	4.479%	$134.1301	$134.13	$134.15	$134.10
Purchase #2	$239.57	6.847%	$255.9734	$255.97	$255.95	$256.00
Purchase #3	$50.97	6.445%	$54.255	$54.26	$54.25	$54.30
Purchase #4	$63.80	12.769%	$71.9466	$71.95	$71.95	$71.90
Purchase #5	$158.58	6.272%	$168.5261	$168.53	$168.55	$168.50
Purchase #6	$240.68	8.189%	$260.3893	$260.39	$260.40	$260.40
Purchase #7	$31.98	11.298%	$35.5931	$35.59	$35.60	$35.60
7 purchase totals =	$913.96		$980.8136	$980.82	$980.85	$980.80