Interest earned in Kenya by a resident individual - from a money market fund, a bank deposit or most government paper - has 15% withholding tax taken off at source, and that is the end of it: no further tax to declare. Infrastructure bonds are the main exception, and are tax-free.
Savings calculator
How savings grow in a money market fund, deposit account or government bond after Kenya's 15% withholding tax on interest.
This shows the arithmetic, not a recommendation. Rates change, and different products carry different risks. See Saving and investing in Kenya.