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	$73.95	10.242%	$81.524	$81.52	$81.50	$81.50
Purchase #2	$132.80	10.182%	$146.3217	$146.32	$146.30	$146.30
Purchase #3	$43.26	9.782%	$47.4917	$47.49	$47.50	$47.50
Purchase #4	$112.83	12.598%	$127.0443	$127.04	$127.05	$127.00
Purchase #5	$210.76	3.366%	$217.8542	$217.85	$217.85	$217.90
Purchase #6	$49.92	11.138%	$55.4801	$55.48	$55.50	$55.50
Purchase #7	$97.38	8.492%	$105.6495	$105.65	$105.65	$105.60
7 purchase totals =	$720.90		$781.3655	$781.35	$781.35	$781.30