My wife is paid a monthly incentive bonus if she reaches the goal of collected money by the end of the month. When her bonus is paid out in combination with her hourly wages, the percentage of taxes withheld adds up to 40%.

What is the normal tax % for an incentive bonus and will we see some of this back in our taxes?

I may be wrong here, but at the end of the year, when its all said and done, money is money.

Whether you made $40,000 in wages, and $10,000 in bonuses, you still made $50,000

If you made $10,000 in wages and $40,000 in bonuses, you still made $50,000.

Im no tax expert, but I can do a short form and all income gets talley'd in the same way. As far as percentage, I would say that it all depends on how much these bonuses add up at the end of the year to determine your tax bracket.
If they are not witholding any money from the bonuses, you'd better be ready to pay in April. Uncle Sam always gets his dollar.

My wife is paid a monthly incentive bonus if she reaches the goal of collected money by the end of the month. When her bonus is paid out in combination with her hourly wages, the percentage of taxes witheld adds up to 40%.

What is the normal tax % for an incentive bonus and will we see some of this back in our taxes?

Tax rate is same if it is for regular salary or bonus. What the employer may be doing is taxing your wife's income based on what they thought is the right tax rate per pay check. That is, when she gets bonus, the company may be withholding the tax at higher income rate. If that is the case, State + Federal tax can easily reach up to 40%.

At the end of the year, you will get your tax refund if you overpaid. If you don't want to overpay during the year, you can ask your employer to withhold less tax.