Bonuses and commission are remuneration, so UIF applies to them the same as to salary. The employee contributes 1% and the employer matches it.
The ceiling is what usually decides the answer in practice. UIF is calculated on remuneration up to a monthly maximum, and anything above that is disregarded. If your ordinary salary already sits at or above the ceiling, a bonus in that month adds nothing to the UIF deducted, because the contribution was already capped.
For someone earning below the ceiling, a bonus does increase UIF for that month, but only up to the cap. The deduction cannot exceed 1% of the ceiling no matter how large the payment.
Some payments fall outside remuneration for UIF purposes entirely, including certain lump sums on retirement or retrenchment. Where a payslip mixes ordinary pay with a severance amount, they are not necessarily treated alike, and it is worth checking the split rather than assuming the whole payment was treated the same way.