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	$230.96	12.851%	$260.6407	$260.64	$260.65	$260.60
Purchase #2	$181.69	12.301%	$204.0397	$204.04	$204.05	$204.00
Purchase #3	$83.63	7.548%	$89.9424	$89.94	$89.95	$89.90
Purchase #4	$239.57	8.622%	$260.2257	$260.23	$260.25	$260.20
Purchase #5	$40.49	12.192%	$45.4265	$45.43	$45.45	$45.40
Purchase #6	$71.62	9.143%	$78.1682	$78.17	$78.15	$78.20
Purchase #7	$135.27	4.295%	$141.0798	$141.08	$141.10	$141.10
7 purchase totals =	$983.23		$1,079.5230	$1,079.53	$1,079.60	$1,079.40