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	$70.36	4.259%	$73.3566	$73.36	$73.35	$73.40
Purchase #2	$122.42	3.511%	$126.7182	$126.72	$126.70	$126.70
Purchase #3	$46.61	10.426%	$51.4696	$51.47	$51.45	$51.50
Purchase #4	$49.32	10.632%	$54.5637	$54.56	$54.55	$54.60
Purchase #5	$128.49	12.556%	$144.6232	$144.62	$144.60	$144.60
Purchase #6	$57.73	8.208%	$62.4685	$62.47	$62.45	$62.50
Purchase #7	$40.89	11.691%	$45.6704	$45.67	$45.65	$45.70
7 purchase totals =	$515.82		$558.8702	$558.87	$558.75	$559.00