How did I get cash shortage on my cash register?

Before you check out of ur cash register your suppose to add the hand written tips because that doesn't come out on the computer but I forgot to do that. I was short $7.77,? I know the $7 was for the written tips but the .77 cents? How do you get cash shortage? %26amp;%26amp; what happens if you do it again?|||If the tips do not register, but you put the money in the cash drawer and forget to enclose your note regarding the hand written tips, the register should be over not short.