Thanks Brian. Sometimes it's really the easiest to directly look into the code although Java is not a know language for me. But Max did a very good readable code, so it was easy to simply add the ROUND() function to the list of codes.

In line 78 of basic.js the function can be added:
this.properties = { mode:["Long","Long","Short"], f:"a+b", preset:["a+b", "a+b", "a-b", "a*b", "a/b", "sin[a]", "cos[a]", "pow(a,b)", "round(a)"], a:[1], b:[1]};

Works now perfect for me.