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	$217.92	10.406%	$240.5968	$240.60	$240.60	$240.60
Purchase #2	$33.28	7.514%	$35.7807	$35.78	$35.80	$35.80
Purchase #3	$123.39	11.389%	$137.4429	$137.44	$137.45	$137.40
Purchase #4	$107.61	4.717%	$112.686	$112.69	$112.70	$112.70
Purchase #5	$66.99	8.265%	$72.5267	$72.53	$72.55	$72.50
Purchase #6	$136.88	12.845%	$154.4622	$154.46	$154.45	$154.50
Purchase #7	$116.46	12.221%	$130.6926	$130.69	$130.70	$130.70
7 purchase totals =	$802.53		$884.1879	$884.19	$884.25	$884.20