total += nValue;

so would that mean that whatever the total is it will be added towards nValue, or is something being incremented?

Thanks

It means

total = total + nValue;
Also you can have
total = total * nValue // total *= nValue
total = total / nValue  // total /= nValue
total = total - nValue  // toatl -= nValue
Some time you can Also have something like thing 
total *= 0.05M; // total = total * 0.05, Note the present of M.
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