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	$25.85	3.849%	$26.845	$26.85	$26.85	$26.80
Purchase #2	$19.71	8.692%	$21.4232	$21.42	$21.40	$21.40
Purchase #3	$112.45	13.633%	$127.7803	$127.78	$127.80	$127.80
Purchase #4	$83.78	4.462%	$87.5183	$87.52	$87.50	$87.50
Purchase #5	$27.30	8.310%	$29.5686	$29.57	$29.55	$29.60
Purchase #6	$35.36	6.832%	$37.7758	$37.78	$37.80	$37.80
Purchase #7	$172.86	8.191%	$187.019	$187.02	$187.00	$187.00
7 purchase totals =	$477.31		$517.9302	$517.94	$517.90	$517.90