If my tab is $5, could I leave a .40 tip?

An appropriate tip is 18% ... $0.90 for a $5 tab.  But that is so cheap. Usually I leave $2 for a $5 tab.

Those who serve you make minimum wage and NEED tips to survive.  Don't be stingy.

But I do not tip unless I have been seated at a table and they are bringing my food, checking up to see if it is okay, and clearing away my plate when I am done.  That is what the tip is for.  For service and personal attention.  Not just taking my order and passing it across the counter to me.

There is NO need to leave a tip for just a $5 tab.

thats very cheap leave at least a dollar

1$ is the proper amount for a 5$ tab.

In America, that tip seems too low. In Japan, you never tip. The Japanese way is better. 

If it's exactly $5 then you leave a dollar. That is 20% and that is plenty, but tipping more than 15% seems excessive to me. 

try one or two dollars....................

Yes, you can leave a 40 cent tip if your tab is $5 dollars.

You could if you want to. I'd leave a dollar.

Sure, or you could tip nothing.  Whatever you want.  I would tip a dollar.

thats up to you