Assuming the inductance is essentially fixed for a given package size, the lower value capacitance will have a higher SRF, around which it will decouple more effectively. Paralleling different values provides a low impedance over the entire range needed.

This Xilinx document (xapp623) goes into great detail on the ins and out of decoupling and why different values are used.

To quote a relevant part - they say:

Capacitor Effective Frequency

Every capacitor has a narrow frequency band where it is most effective as a decoupling capacitor. Outside this band, it does have some contribution to the PDS but in general it is much smaller. The frequency bands of some capacitors are wider than others. The ESR of the capacitor determines the quality factor (Q) of the capacitor, which determines the width of the effective frequency band. Tantalum capacitors generally have a very wide effective band, while X7R and X5R chip capacitors, with their lower ESR, generally have a very narrow effective band. The effective frequency band corresponds to the capacitor's resonant frequency. While an ideal capacitor only has a capacitive characteristic, real non-ideal capacitors also have a parasitic inductance ESL and a parasitic resistance ESR. These parasitics act in series to form an RLC circuit (Figure 3). The resonant frequency associated with that RLC circuit is the resonant frequency of the capacitor.

Assuming the inductance is essentially fixed for a given package size, the lower value capacitance will have a higher SRF, around which it will decouple more effectively. More than one of each value reduces inductance/ESR to lower impedance around this frequency. Sets of different values provides a low impedance over the entire range needed.

This Xilinx document (xapp623) goes into great detail on the ins and out of decoupling and why different values are used.

To quote a relevant part - they say:

Capacitor Effective Frequency

Every capacitor has a narrow frequency band where it is most effective as a decoupling capacitor. Outside this band, it does have some contribution to the PDS but in general it is much smaller. The frequency bands of some capacitors are wider than others. The ESR of the capacitor determines the quality factor (Q) of the capacitor, which determines the width of the effective frequency band. Tantalum capacitors generally have a very wide effective band, while X7R and X5R chip capacitors, with their lower ESR, generally have a very narrow effective band. The effective frequency band corresponds to the capacitor's resonant frequency. While an ideal capacitor only has a capacitive characteristic, real non-ideal capacitors also have a parasitic inductance ESL and a parasitic resistance ESR. These parasitics act in series to form an RLC circuit (Figure 3). The resonant frequency associated with that RLC circuit is the resonant frequency of the capacitor.