As I See It: Even Thousands of GP

Every adventurer isn't rain man. They look at a heap of coins and say "That looks like 600 GP to me." It's a form of significant figure and with all things being equal, as we assume that adventurers are competent at adventuring matters, all of their estimated coin totals total up to something that's close enough to the actual realistic total that it's not worth slowing down the game to worry about it.

The same way that we don't have things like "Hit Points: blood left: 47543.26 millilitres; compound fracture of left anterior tibia; 2nd degree burn on upper right arm from fingertips to shoulder" and "Sword, long, steel, high carbon, 54 rockwell hardness, blade length: 107.5 cm, entire length: 129.2 cm, single-edged, hollow-grind; sharpness: 63% of maximum; weight: 8.2 kg" on our character sheets for heck's sake.

If say, a theoretical DM, decided that even thousands of coin was unrealistic and would subtract 500 coins and add a d1000 roll to have true scientific realistic treasure hoards, they would find out pretty dang soon that it's a pain in the ass for the DM and the players to deal with that degree of accuracy. Not that I ever learned that lesson the hard way...