Each band's rate applies to income above its threshold, up to the next band.
VAT/sales-tax results are exact for the rate you enter. Nothing is uploaded.
Income-tax presets are simplified estimates (Kenya PAYE bands incl. KES 2,400/mo personal relief, as of recent rules) and ignore NSSF/SHIF, allowances and reliefs. For anywhere else use Custom brackets. Always confirm with your tax authority or employer.