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	$19.78	3.106%	$20.3944	$20.39	$20.40	$20.40
Purchase #2	$127.35	3.863%	$132.2695	$132.27	$132.25	$132.30
Purchase #3	$54.92	10.250%	$60.5493	$60.55	$60.55	$60.50
Purchase #4	$94.56	8.849%	$102.9276	$102.93	$102.95	$102.90
Purchase #5	$133.39	13.245%	$151.0575	$151.06	$151.05	$151.10
Purchase #6	$82.89	13.257%	$93.8787	$93.88	$93.90	$93.90
Purchase #7	$139.47	5.321%	$146.8912	$146.89	$146.90	$146.90
7 purchase totals =	$652.36		$707.9682	$707.97	$708.00	$708.00