My website/e-junkie system has been stable for some time.
I sell small items for $.95 each. I put 75 in the cart, the price calcs to $71.25.
If I change the quantity to 10, the price should go to $9.50 (more or less). It stays above $70. Can't check the exact amount because I had to take my cart offline.
If I change the quantity to 500, the total shoots up.
Reducing the quantity to 10 again doesn't appreciably change the price. It's still shows up in the hundreds of dollars.