[mafuyu]

I think you need to look at it holistically and place yourself in the shoes of your audience. I imagine an example of a "rational" purchase to be something like searching for a good (eg. headphones) on Amazon and comparing prices between brands. A buyer will try to research and justify their purchase, and the cents may help push them over the edge and convince them that they've "done their homework". Meanwhile, an example of the syllable tactic is a restaurant menu. When I order from a menu, I'm time constrained and forced into a decision. I ask myself internally: "Would I get 19 dollar value from this meal?", and if the answer is "Yes", I'll order it.