Indeed. The standard calculator application loads very fast. Downloading a java calculator would be sort of inconvenient, as you would have to boot up the application everytime you want to use it.
Or just do the math in your head. The easy way is to figure for 10 percent (move decimal over one place), then take that value and add half of it to itself. Example:
6.23 x 10 = .62
.62/2 = .31
.62 + .31 = .93
Looks complicated, but very simple to do in your head if you give it a try.