Lets say that you sold the share when it is $4.30. That would give you a profit of $430 - $418 = $12 Lets factor in the commissions now which would be $25 dollars for both buying and selling.
$12 - $25 - $25 = $38 (Loss)
You made a loss even though the market went in your favour. This means that to break-even in this situation, you would need the share to move by $0.50 before you even start earning any profits.
However, if you were to buy 1000 shares instead of 100, the net profit for selling at $4.30 would be $120 - $25 - $25 = $70 (Profit)
$70 dollars profit might sound good enough, but in terms of percentage, you have only made 1.67% of your capital ($4180). The commissions alone ate up almost half of your profits!
In conclusion, having more capital to begin with would ensure that your profits justifies the amount of risk they you are going to take as well as the cost that will be incurred. The cost mentioned here is just the commission fees, there are also other cost such as GST, service fees etc. Always make sure that you have considered such costs into your decision in buying shares or you could actually end up with a loss!
As always, if you have any questions, feel free to leave a comment.