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	$9.41	10.443%	$10.3927	$10.39	$10.40	$10.40
Purchase #2	$46.45	7.398%	$49.8864	$49.89	$49.90	$49.90
Purchase #3	$165.71	11.644%	$185.0053	$185.01	$185.00	$185.00
Purchase #4	$93.92	10.223%	$103.5214	$103.52	$103.50	$103.50
Purchase #5	$34.27	3.120%	$35.3392	$35.34	$35.35	$35.30
Purchase #6	$206.96	12.608%	$233.0535	$233.05	$233.05	$233.10
Purchase #7	$13.46	13.810%	$15.3188	$15.32	$15.30	$15.30
7 purchase totals =	$570.18		$632.5173	$632.52	$632.50	$632.50