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	$235.92	8.203%	$255.2725	$255.27	$255.25	$255.30
Purchase #2	$142.96	10.406%	$157.8364	$157.84	$157.85	$157.80
Purchase #3	$10.82	13.168%	$12.2448	$12.24	$12.25	$12.20
Purchase #4	$76.52	12.330%	$85.9549	$85.95	$85.95	$86.00
Purchase #5	$102.55	13.535%	$116.4301	$116.43	$116.45	$116.40
Purchase #6	$137.53	5.325%	$144.8535	$144.85	$144.85	$144.90
Purchase #7	$56.70	8.177%	$61.3364	$61.34	$61.35	$61.30
7 purchase totals =	$763.00		$833.9286	$833.92	$833.95	$833.90