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	$107.90	11.691%	$120.5146	$120.51	$120.50	$120.50
Purchase #2	$76.38	7.108%	$81.8091	$81.81	$81.80	$81.80
Purchase #3	$29.62	5.518%	$31.2544	$31.25	$31.25	$31.30
Purchase #4	$99.62	11.857%	$111.4319	$111.43	$111.45	$111.40
Purchase #5	$95.25	9.351%	$104.1568	$104.16	$104.15	$104.20
Purchase #6	$80.40	3.271%	$83.0299	$83.03	$83.05	$83.00
Purchase #7	$176.36	10.472%	$194.8284	$194.83	$194.85	$194.80
7 purchase totals =	$665.53		$727.0251	$727.02	$727.05	$727.00