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	$233.61	9.300%	$255.3357	$255.34	$255.35	$255.30
Purchase #2	$131.42	7.765%	$141.6248	$141.62	$141.60	$141.60
Purchase #3	$129.98	10.378%	$143.4693	$143.47	$143.45	$143.50
Purchase #4	$8.75	8.414%	$9.4862	$9.49	$9.50	$9.50
Purchase #5	$116.86	8.721%	$127.0514	$127.05	$127.05	$127.10
Purchase #6	$65.82	9.863%	$72.3118	$72.31	$72.30	$72.30
Purchase #7	$16.79	12.390%	$18.8703	$18.87	$18.85	$18.90
7 purchase totals =	$703.23		$768.1495	$768.15	$768.10	$768.20