You would do so the same as you would if you were only uploading one file.
driver.findElement(By.id("input1")).sendKeys("path/to/first/file");
driver.findElement(By.id("input2")).sendKeys("path/to/second/file");
driver.findElement(By.id("input3")).sendKeys("path/to/third/file");
driver.findElement(By.id("input4")).sendKeys("path/to/fourth/file");
driver.findElement(By.id("input5")).sendKeys("path/to/fifth/file");
driver.findElement(By.id("upload")).click();
Obviously, you'll need to put in your own correct IDs or whatever.