How can I apply a 25% blanket discount to everything in my store

[Relicroadtx]

I have about 150 items in my store and I want to offer 25% off everything. Is there a way I can do this without having to manually change every item description? Thanks.

[Kswitten]

Its not exactly the same but what if you just did a 25% off coupon code and had the coupon code as a pop up so everyone sees it when they log on to shop