User blog comment:Sam Wang/BTD5 - Tips For Reaching High Rounds/@comment-5056929-20120808071740

Supply Drop Snipers

Actually, Supply Drop Snipers are very useful in the late rounds, they may be expensive at first but they will pay off. They are a better option for later rounds as banana farms only generate the same amount of money per round no matter how long it is (Later rounds could take several minutes) and they cover a lot of space too, making them impractical for later rounds. the Supply Drop Snipers have a specific recharge time so the longer the round, the more money you earn from them.

Regen Bloon Exploit

Performing the regen exploit on round 76 will give you a huge economical advantage, I'm pretty sure someone on the NK forums has made a much better explanation but it basically involves using master of airs to duplicate the regen ceramics repetitively.

Extreme Farming

Try to fill the whole screen with 4-2 farms ASAP, doing this will help HEAPS when preparing for the freeplay rounds.

The way that can guaranteed you winning any round no matter what

A completely different setup involves continuously buying, using the ability and selling Techno Terrors can take down ZOMGs when used 5-6 times and can kill BFBs in an instant, supply drop snipers are still recommended. However, this can be very tedious and you'll get bored quickly.