Download Progress Calculator
It's really hard to tell what this class does. From what you say, I feel like you have a number of TransferTasks and want to have a sort of ProgressTracker for them. So, as for me, your goal is to make user's code look like this:

ProgressTracker progressTracker = new ProgressTracker();
progressTracker.setListener(new ProgressTrackerListener() {
  @Override
  public void onProgressChanged(double progressPercentage) {
    // TODO: update your UI here
  }
});
...
TransferTask transferTask = new UploadTask("/home/jiduvah/1.txt");
progressTracker.track(transferTask);
transferTask.start();


Why? Because it doesn't need any comments to describe what happens here: you just write it in English.

Update - In case you're absolutely sure you like your approach.

First, in this code:

private int round(int num) {
    int temp = num % 5;
    if (temp &lt; 3)
        return num - temp;
    else
        return num + 5 - temp;
}


I see magic like 5 and 3. Looks like it does exactly what you need to do, and you've even wrote about meaning of 5, but 3 is still a mystery.

Then:

double x = progressAmount;
double y = totalAmount;
double result = (x / y) * 100;
return (int) result;


When you divide int by int, you get int. When you divide int by double or double by int, you get double. So you may just write:

double result = 100 * progressAmount / (double)totalAmount;


Regarding the whole idea, I'm not sure whether this code works at all, because it's hard to understand how one should use it.