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	$100.78	10.285%	$111.1452	$111.15	$111.15	$111.10
Purchase #2	$196.77	9.590%	$215.6402	$215.64	$215.65	$215.60
Purchase #3	$28.46	10.439%	$31.4309	$31.43	$31.45	$31.40
Purchase #4	$192.81	11.831%	$215.6214	$215.62	$215.60	$215.60
Purchase #5	$12.51	8.662%	$13.5936	$13.59	$13.60	$13.60
Purchase #6	$7.39	13.341%	$8.3759	$8.38	$8.40	$8.40
Purchase #7	$67.97	9.331%	$74.3123	$74.31	$74.30	$74.30
7 purchase totals =	$606.69		$670.1195	$670.12	$670.15	$670.00