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	$53.67	5.321%	$56.5258	$56.53	$56.55	$56.50
Purchase #2	$224.94	8.206%	$243.3986	$243.40	$243.40	$243.40
Purchase #3	$111.89	10.397%	$123.5232	$123.52	$123.50	$123.50
Purchase #4	$188.42	10.824%	$208.8146	$208.81	$208.80	$208.80
Purchase #5	$13.69	9.570%	$15.0001	$15.00	$15.00	$15.00
Purchase #6	$149.60	4.666%	$156.5803	$156.58	$156.60	$156.60
Purchase #7	$59.81	10.765%	$66.2485	$66.25	$66.25	$66.20
7 purchase totals =	$802.02		$870.0911	$870.09	$870.10	$870.00