Which pricing strategy is known as 'charm pricing' and has been shown to increase sales by an average of 24% compared to rounded prices?

Pricing strategy is both art and science, with psychological tactics that can significantly impact consumer behavior. One particular pricing technique has proven so effective that it's become ubiquitous in retail environments worldwide. This poll tests your knowledge of a specific psychological pricing tactic that has been validated through decades of market research and consumer behavior studies. Can you identify the strategy that major retailers consider most effective for maximizing perceived value without sacrificing profit margins?

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Prices ending in .99 (e.g., $9.99 instead of $10.00)
Bundle pricing with a 'free' item included (e.g., 'Buy one, get one free')
Prestige pricing (deliberately pricing higher than competitors to signal quality)
Decoy pricing (adding a third, less attractive option to make the target option seem better)