NO!!! It depends on what the current bidder has bid. Let's use your $200 item as an example. Now let's say that $200 bid is mine, and the bid increment for the auction is $5. I may have bid $250, but because no one else has bid, or because my bid is currently the high bid, the auction reads the minimum required "high" bid of $200. Then you put in your bid for $300. EBay will now show your bid as the highest bid - at $255, or $5 above my highest bid.
If there were no bids and the item is listed at a starting bid of $200 or if my bid was for only $200, then yes, your $300 bid would only be posted at the starting bid of $200 or at $205 to top my bid.