Exness minimum deposit in zar depends on the current usdzar exchange rate. The Exness minimum deposit is usually $10 so when you convert to zar at today's usdzar rate of 17.82 zar to 1 usd, then the Exness minimum deposit as at today becomes 178.2 ZAR.
Also note that if your Exness account currency is not set to zar, then you will be charged a currency conversion fee to convert your zar deposit into whatever your account currency is.
Exness may not show you what the currency conversion fee is, as they just include it into the usdzar rate.