...They call it sacrificial giving...
I call it unbiblical.
Let us examine the passage using a real Bible (Authorized King James):
Luke 21:1-4 King James Version (KJV)
And he looked up, and saw the rich men casting their gifts into the treasury.
And he saw also a certain poor widow casting in thither two mites.
And he said, Of a truth I say unto you, that this poor widow hath cast in more than they all:
For all these have of their abundance cast in unto the offerings of God: but she of her penury hath cast in all the living that she had.
If the rich men gave 15, 25, or even 50% of everything they had they still would not be a 'sacrificial giver'; because they give 'out' of their abundance not 'according' to it.
What did God tell the rich man? Sell some of what you have and follow me?
Mark 10:21 King James Version (KJV)
Then Jesus beholding him loved him, and said unto him, One thing thou lackest: go thy way, sell whatsoever thou hast, and give to the poor, and thou shalt have treasure in heaven: and come, take up the cross, and follow me.
The rich man, like the rich tithers, believed that he was righteous in and of himself claiming "I have kept all of the commandments". So Jesus said, paraphrased of course, "ok then, lets go down the checklist":
1. You shall have no other gods before Me.
"If God is truly first, then sell everything you have...and follow me"
1 Samuel 16:7King James Version (KJV)
But the Lord said unto Samuel, Look not on his countenance, or on the height of his stature; because I have refused him: for the Lord seeth not as man seeth; for man looketh on the outward appearance, but the Lord looketh on the heart.
When a pastor calls giving more than 10% (but less than 100%) 'sacrificial giving' it shows that he does not know what he is talking about.
Now it is not God's will that you sell everything that you have and give it to the poor. He simply wants you to recognize that your righteousness is in Him (Jesus Christ) alone; that apart from him you can do no good.