I write it in on the receipt for both.
The MSC can see what I did tip and the actual total with the tip added. Can be important when it is a reimbursement shop up to $XX (vs. flat fee regardless of how much is spent) or some shops require you to tip XX%.
I do it for me so I'm keeping track of what I spent vs. paid. If I did everything to stay within the guidelines but the reimbursement + fee (if any) does not cover, I want to write any negative difference off on my taxes.
Same is true on a shop paid with a credit or debit card. You don't get another receipt after you write in the tip and final total on the merchants copy. Just pen it in and total on the customer receipt too and submit to MSC.
Sometimes the receipt doesn't give a detailed view of what was ordered and most MSC"s want to see that.
Lay that receipt next to the customer copy of the charge receipt (with written in tip and grand total), take as 1 picture, and submit to the MSC as the receipt.
@Boutique wrote:
You write it on the receipt? Just for your own reference or for the MS company?