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	$66.86	11.409%	$74.4881	$74.49	$74.50	$74.50
Purchase #2	$123.40	8.594%	$134.005	$134.01	$134.00	$134.00
Purchase #3	$52.82	12.497%	$59.4209	$59.42	$59.40	$59.40
Purchase #4	$176.66	13.653%	$200.7794	$200.78	$200.80	$200.80
Purchase #5	$131.29	8.528%	$142.4864	$142.49	$142.50	$142.50
Purchase #6	$218.40	8.798%	$237.6148	$237.61	$237.60	$237.60
Purchase #7	$199.77	13.274%	$226.2875	$226.29	$226.30	$226.30
7 purchase totals =	$969.20		$1,075.0821	$1,075.09	$1,075.10	$1,075.10