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	$245.73	8.218%	$265.9241	$265.92	$265.90	$265.90
Purchase #2	$250.65	11.715%	$280.0136	$280.01	$280.00	$280.00
Purchase #3	$171.82	13.572%	$195.1394	$195.14	$195.15	$195.10
Purchase #4	$142.60	13.287%	$161.5473	$161.55	$161.55	$161.50
Purchase #5	$139.90	3.240%	$144.4328	$144.43	$144.45	$144.40
Purchase #6	$195.82	13.353%	$221.9678	$221.97	$221.95	$222.00
Purchase #7	$37.70	4.473%	$39.3863	$39.39	$39.40	$39.40
7 purchase totals =	$1,184.22		$1,308.4113	$1,308.41	$1,308.40	$1,308.30