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	$87.87	13.734%	$99.9381	$99.94	$99.95	$99.90
Purchase #2	$44.73	4.591%	$46.7836	$46.78	$46.80	$46.80
Purchase #3	$13.74	13.716%	$15.6246	$15.62	$15.60	$15.60
Purchase #4	$38.79	11.464%	$43.2369	$43.24	$43.25	$43.20
Purchase #5	$203.93	11.492%	$227.3656	$227.37	$227.35	$227.40
Purchase #6	$34.26	12.674%	$38.6021	$38.60	$38.60	$38.60
Purchase #7	$20.72	4.694%	$21.6926	$21.69	$21.70	$21.70
7 purchase totals =	$444.04		$493.2435	$493.24	$493.25	$493.20