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	$13.80	13.141%	$15.6135	$15.61	$15.60	$15.60
Purchase #2	$78.81	10.169%	$86.8242	$86.82	$86.80	$86.80
Purchase #3	$60.61	4.840%	$63.5435	$63.54	$63.55	$63.50
Purchase #4	$36.49	3.747%	$37.8573	$37.86	$37.85	$37.90
Purchase #5	$122.88	13.225%	$139.1309	$139.13	$139.15	$139.10
Purchase #6	$247.87	3.868%	$257.4576	$257.46	$257.45	$257.50
Purchase #7	$42.46	3.554%	$43.969	$43.97	$43.95	$44.00
7 purchase totals =	$602.92		$644.3960	$644.39	$644.35	$644.40