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	$122.62	13.392%	$139.0413	$139.04	$139.05	$139.00
Purchase #2	$9.79	10.833%	$10.8506	$10.85	$10.85	$10.90
Purchase #3	$138.28	4.488%	$144.486	$144.49	$144.50	$144.50
Purchase #4	$34.65	7.136%	$37.1226	$37.12	$37.10	$37.10
Purchase #5	$100.70	10.838%	$111.6139	$111.61	$111.60	$111.60
Purchase #6	$21.70	7.248%	$23.2728	$23.27	$23.25	$23.30
Purchase #7	$176.36	3.833%	$183.1199	$183.12	$183.10	$183.10
7 purchase totals =	$604.10		$649.5071	$649.50	$649.45	$649.50