Thanks to Rich_Roast from the Peppermint OS forum for helping me to become aware of the built in calculator. I worked out the tutorial.
Peppermint One has Galculator installed by default, while ICE seems to have none. However, xcalc is installed. To run it,
click Menu > Run
and type in xcalc
If you want a shortcut to Xcalc in your accessories menu:
go to folder /usr/share/applications
click on Tools > Open current folder as root and enter your password.
run Leafpad, to do this click Menu > Accessories > Leafpad
type the following into the window:
save the file as xcalc.desktop to the desktop folder
right click the file, click on move
go back to PCManFm and click on Edit and then on Paste
You have now pasted the file to the /usr/share/applications folder and you have a shortcut to xcalc in Accessories. Note that we are "borrowing" the kcalc icon as xcalc does not have an icon in the file.
Alternatively (if you want to easier solution, and you have an Internet connection) you can install Galculator
Click on Menu
type in: sudo apt-get galculator
type in your root password and press ENTER
you now have Galculator added to your Accessories menu.
For a different approach try Speedcrunch, it is very suitable as a financial calculator. It's great to have options.