Bartering with a 3 year old

My husband occasionally barters with our 3 year old about going places or doing something. For example, he'll say she has to go to bed in 3 minutes. She counters with 10 minutes. He says 4, she sticks with her trusty 10. This continues...until he suddenly jumps to 15 minutes, in which she puts her hands on her hips (btw that's new this week) and says, 10 one last time (you'd think he's stop here...). Josh says 10 back at her and then she says, "No 3 minutes Daddy!" Works every time.