Mythbusters put it to the test:

https://mythresults.com/laws-of-attraction

Kari volunteered to work in a coffee shop, disguising her appearance with a wig and makeup and using three different bust sizes: “small” (taped down to achieve a reduction of two cup sizes), “medium” (no alteration), and “large” (DDD size). Grant and Tory watched her through hidden cameras and gave her a tip jar rigged to separate tips given by men from those given by women.

They focused on the tips Kari collected from the first 80 male customers on each shift. During the “small” and “medium” shifts, she collected $72 in tips, while the “large” shift yielded $98, with both men and women tipping almost 40% more. The team classified the myth as confirmed.