Hi Govardhan
I think what you want to do is create a Print Format
Go to Document (top bar - 2nd icon) > New > Print Format.
As an example, have a look at "Sales Invoice Classic/Modern/Spartan". It is done using code.
Rounded Total rounds the Grand Total to a whole number. You can hide the Rounded Total field and instead add a similar style to Grand Total, or for printing purposes, you can use flt(doc.grand_total_export, 2) to round grand total value to 2 decimal places and use it to display Round Total.
Thanks,
Anand.