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	$183.31	11.866%	$205.0616	$205.06	$205.05	$205.10
Purchase #2	$96.75	4.205%	$100.8183	$100.82	$100.80	$100.80
Purchase #3	$114.75	5.348%	$120.8868	$120.89	$120.90	$120.90
Purchase #4	$18.46	13.138%	$20.8853	$20.89	$20.90	$20.90
Purchase #5	$215.44	3.184%	$222.2996	$222.30	$222.30	$222.30
Purchase #6	$48.52	5.371%	$51.126	$51.13	$51.15	$51.10
Purchase #7	$108.52	10.113%	$119.4946	$119.49	$119.50	$119.50
7 purchase totals =	$785.75		$840.5722	$840.58	$840.60	$840.60