The Dead Sea scrolls were almost identical to current scrolls. There were few differences mainly change in shape of the same letter. The Scribes would add up the values of the letters in all the lines and columns to look for errors. Temple scrolls were perfect. I don’t believe that all the scrolls are in error.
Here is an interesting article about scribes and texts.
http://www.godandscience.org/apologetics/bibleorg.html
There are reportedly 3,536,489 letters in the Bible. (I didn't count them, I looked it up!) If the text is 99.5% error free, that makes 17,687 errors. And there are indeed thousands of scribal errors in the various mss of scripture.
However, I do not derive a skeptical attitude about the Bible from those calculations. The truth is that the Bible is rather astoundingly error-free, compared to any other ancient text. Even more important, most of these scribal errors make no difference whatsoever. For instance, one text says "he had sheep and goats," another says "he had goats and sheep", and the Aramaic is over there saying "he had herds and flocks."
Lots of variants, makes no difference at all.
People who play up scribal errors to encourage agnosticism (like Bart Ehrman) are, in my view, pedantic fools. They turn "perfect text" into a kind of an idol, and then when they find a half-penny variant, they say "There is no god!"