People that love numbers! I need your help! :)

I just started trading based off of round numbers. I love it! I have an indicator that posts on the eur/usd and it posts the major every 1k pips the medium ever 100 and the small at every 50.

EX) Major : 1.700 Medium: 1.7100 Small : 1.6050

So my question is.. how do you know where to place them? Is there a percentage I could use on any number to figure out if I need to go up by 10s or 5s or 50s etc?

I want to trade this using stocks and lots of stocks are below 10$ so I don't know which round numbers you use? So.. I would love if someone could help me figure this out
THanks guys!!!

Pound pairs /EURGBP, GBPCHF, GBPJPY and GBPUSD too/ love 50's and 00's.
Good idea to put targets to 5 pips above / below them, like 139.45 for GBPJPY or 1.5995 for GBPUSD, you know what I mean.

How do you know? Spend a couple hundred or thousand hours in front of that screen and you'll get into the swing of it.