If you are just doing general off hand shooting, don't worry about it too much. As hard as you try, you will lose some when you pour, some will stick to the inside of the barrel on the way down, etc., etc. If you are bench shooting I suppose you may need to get more finicky about the exact size of the charge... for general off hand you probably aren't going to notice the difference between 60 grains and 57 grains. You might, its just not likely... other variables will probably overshadow any difference.
Ditto on trying to do it the same way every time, however, which will help minimize variation. I don't tap my measure myself, but nothing says you can't... just do it that way every time. Controlled variation can be useful, uncontrolled variation is generally not a good thing in shooting. My advice is to "be as careful as you reasonably can" in measuring. If you get too silly about it, one of your fellow shooters will give you a mountain name like "Old Persnickety", which you may or may not find peferrable to other options they have in mind.
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