So, all that $ we gave to nefarious causes (twi).  Well I trust GOD that he knew our hearts and that goes towards our accounts. 
Now, I/we know better and choose who we donate to. 
Bottom line: just give and don't try to figure out the %. 
Rocky is right on in my thinking with the verse, be cheerfull about it.  If you ain't, then don't and find a place and amount that makes you cheerfull.