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	$68.46	5.667%	$72.3396	$72.34	$72.35	$72.30
Purchase #2	$153.40	9.761%	$168.3734	$168.37	$168.35	$168.40
Purchase #3	$47.81	13.387%	$54.2103	$54.21	$54.20	$54.20
Purchase #4	$217.26	11.262%	$241.7278	$241.73	$241.75	$241.70
Purchase #5	$48.55	6.288%	$51.6028	$51.60	$51.60	$51.60
Purchase #6	$38.45	3.422%	$39.7658	$39.77	$39.75	$39.80
Purchase #7	$206.67	4.523%	$216.0177	$216.02	$216.00	$216.00
7 purchase totals =	$780.60		$844.0374	$844.04	$844.00	$844.00