Price breaks depending on quantity

[MacPhotoBiker]

Hi,

is it possible to maintain several purchasing costs for one and the same article depending on quantities ("Price Breaks"), e.g.:

10 pcs: $5/ pc.
20 pcs: $4/pc.
50 pcs. $3/pc.

I tried to set up different prices for the same article with different quantities, but I got a key constraint error (because every article can only be set up once).

How could I set up the above example in both the purchase and the sales module?

Thanks a lot!