If you want to charge:
$0.08 for the 1st 3 minutes of a call and
$0.05 for each additional minute
Then, you should enter:

and

The IDI platform computes the charges so that a call that lasts exactly 3 minutes would be charged $0.08. Calls that last longer than 3 minutes would be charged $0.08 for the first 3 minutes and $0.05 for each additional minute. Based on $0.08 for 3 minutes (180 rate seconds), the per minute rate for the initial time is $0.0266666; and $0.15 for 3 minutes (180 rate seconds), the per minute rate for the additional time is $0.05.
Example calls:
3 minute call
3 * $0.0266666 = $0.08
initial time multiplied by the per minute rate
5 minute call
(3 * $0.0266666) + (2 * $0.05) = $0.18
initial time multiplied by the initial per minute rate plus additional time multiplied by the additional per minute rate
1.5 minute call
2 * $.0266666 = $0.0533 (rounded)
initial time multiplied by the initial per minute rate