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	$30.97	12.472%	$34.8326	$34.83	$34.85	$34.80
Purchase #2	$59.75	11.854%	$66.8328	$66.83	$66.85	$66.80
Purchase #3	$59.58	9.130%	$65.0197	$65.02	$65.00	$65.00
Purchase #4	$65.28	8.481%	$70.8164	$70.82	$70.80	$70.80
Purchase #5	$214.43	6.711%	$228.8204	$228.82	$228.80	$228.80
Purchase #6	$92.35	12.524%	$103.9159	$103.92	$103.90	$103.90
Purchase #7	$220.40	6.379%	$234.4593	$234.46	$234.45	$234.50
7 purchase totals =	$742.76		$804.6971	$804.70	$804.65	$804.60