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	$20.40	8.698%	$22.1744	$22.17	$22.15	$22.20
Purchase #2	$160.80	7.285%	$172.5143	$172.51	$172.50	$172.50
Purchase #3	$35.86	4.437%	$37.4511	$37.45	$37.45	$37.50
Purchase #4	$31.53	10.144%	$34.7284	$34.73	$34.75	$34.70
Purchase #5	$89.37	3.117%	$92.1557	$92.16	$92.15	$92.20
Purchase #6	$119.25	13.160%	$134.9433	$134.94	$134.95	$134.90
Purchase #7	$116.95	8.140%	$126.4697	$126.47	$126.45	$126.50
7 purchase totals =	$574.16		$620.4369	$620.43	$620.40	$620.50