system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do coupons have a 'cash' value of 1/20¢?
gpt
Before there were coupons, stores encouraged people to shop by offering trading stamps, where for every dime you spent at the store, you got a stamp, and when you saved enough stamps, you can mail in those stamps for free merchandise (Kind of like an analog version of air mile points). These stamps were HUGE business back in the early to mid 1900s.

But merchants had to pay the stamp makers for the stamps and that payment increased prices of goods, customers who didn't collect stamps thought that the price increase was unfair so Congress decreed that the stamps had to have cash value so that customers can redeem them directly with the merchant for money (thereby offsetting the increase in good prices). And the 1/20 of one cent was a considered a fair price back in the early 1900s (it's enough to shut the complainers up, but not enough to damage the stamp-maker's business). In certain states, coupons are still considered trading stamps, so by law, they have to include the disclaimer.