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	$31.99	5.825%	$33.8534	$33.85	$33.85	$33.90
Purchase #2	$183.81	5.757%	$194.3919	$194.39	$194.40	$194.40
Purchase #3	$28.26	10.703%	$31.2847	$31.28	$31.30	$31.30
Purchase #4	$97.46	12.689%	$109.8267	$109.83	$109.85	$109.80
Purchase #5	$12.60	4.716%	$13.1942	$13.19	$13.20	$13.20
Purchase #6	$114.89	12.190%	$128.8951	$128.90	$128.90	$128.90
Purchase #7	$153.88	10.481%	$170.0082	$170.01	$170.00	$170.00
7 purchase totals =	$622.89		$681.4542	$681.45	$681.50	$681.50