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	$26.98	7.861%	$29.1009	$29.10	$29.10	$29.10
Purchase #2	$121.83	3.808%	$126.4693	$126.47	$126.45	$126.50
Purchase #3	$87.96	10.277%	$96.9996	$97.00	$97.00	$97.00
Purchase #4	$31.48	12.844%	$35.5233	$35.52	$35.50	$35.50
Purchase #5	$233.99	13.777%	$266.2268	$266.23	$266.25	$266.20
Purchase #6	$154.45	8.857%	$168.1296	$168.13	$168.15	$168.10
Purchase #7	$244.62	4.596%	$255.8627	$255.86	$255.85	$255.90
7 purchase totals =	$901.31		$978.3122	$978.31	$978.30	$978.30