So after I changed my lay only trigger I've successfully layed 111 markets today all with low stakes. We might all have different opinions but my problem has definitely been resolved. For me laying small stakes from odds around 3 to 5, it wasn't a rounding problem or even/odd amounts, it was;
1p to 19p rejected
20p to 31p accepted
32p to 39p rejected
39p+ accepted
So I used this expression;
IF(my_stake < 0.2,0.2,IF(AND(my_stake > 0.31,my_stake < 0.36),0.31,IF(AND(my_stake > 0.35,my_stake < 0.4),0.4,my_stake)))
This changes any stake;
Between 1p and 19p = 20p
Between 20p and 31p = no change
Between 32p and 35p = 31p
Between 36p and 39p = 40p
40p and above = no change
As I said, today I've had no problems and made a profit, I hope this might help someone else but I don't think it will help in dutching.