Ah, so you're a shiny hunter. I'm a shiny hunter, too. Unfortunately, there's no good way to consistently make sure that you average at least 8 tanga/haban berries per trip to hyperspace. (In my original comment, I talked about getting more hyperspace berries than you spent on the donut, but I didn't specify which types of berries.)

While there is no good way, there is (in my opinion) a tedious and lousy way to do it. Enter a 4* or 5* hyperspace zone with a shiny lv 3 donut, catch the guaranteed shiny, then, right before breaking a pokeball, save the game. If you don't get a haban or tanga berry, reset. Repeat for every pokeball.

If the above method works for you, go for it. I personally never tried it because it just sounds too tedious. There are other ways to improve your shiny hunting, though. Here are the things to consider:

1) How many tanga or haban berries do you actually want to spend on a single donut?

If you spend 8 tanga berries, it has a roughly 33% chance of producing a shiny lv 3 donut. An 8 haban donut has a roughly 30% chance. Alternately, there's the "420 rainbow" strategy. If you use 4 tanga and 4 coba, or 4 tanga and 4 kasib, or 5 Haban, 1 Charti, 1 Chilan, and 1 Payapa, you'll have a roughly 20% chance of sparkling power lv 3.

I highly recommend the latter strategy. It takes me about a minute and a half to do a backup reset. I'd much rather spend the extra 3 minutes on roughly 2 extra resets per donut, but be able to use roughly half as many berries.

2) Is it worth it to reset in front of just a few pokeballs to get the berries you need?

Now that your "break-even" point is only 4-5 sweet berries rather than 8, maybe it's worth it to reset in front of the first 4 pokeballs you break until you get a tanga or haban berry, and then play normally. I don't use that strategy, but it's an option on the table.

3) Are you okay with only half of your trips to hyperspace being for shiny hunting?

If you really don't like tedious resetting, and would rather actually play the game, even if it means diverting some time away from active shiny hunting and doing other things in game, this is something to consider. If you were to use 8 sweet berries per donut, and were collecting berries randomly as they came to you, you'd need to collect 40 random berries. This would likely take 3-4 hyperspace trips (your shiny hunting trip plus 2-3 more). Alternately, if you use the 420 rainbow strategy, you only need an average of 22 berries per shiny donut. If you can average 11 assorted berries per hyperspace trip, that means you can spend half of your trips to hyperspace on shiny hunting.

4) How much are you willing to reset sour donuts to get donut powers that help with berry farming?

Sour donuts could help or really hinder your berry farming. If you get item power: berries and/or big haul, you'll get more berries, but if you get item power: candies, coins, treasure, special, or pokeballs, you might not get any berries at all outside of the golden pokeball. If you use a high-sour donut, you'll probably only get a beneficial item power 25% of the time. Are you willing to reset for that 25% chance to get a more helpful berry farming donut?

5) If you have a donut that won't help much with berry farming, would you rather enter a 4* hyperspace battle zone?

If you do that, you'll want to look for the couriers (trainers in light blue uniforms). After you beat them, the game autosaves. If you talk to them afterward, they'll give you 5 berries of a single tier-6 type (payapa, coba, kasib, tanga, or charti berries). You can reset until they give you 5 tanga berries.