Calculating the frequency of data lines?
The "multiply by 5" suggestion would be a way to estimate the oscilloscope bandwidth required to get a good-fidelity waveform display. That's way overkill in terms of the minimum bandwidth required to transfer the data reliably.

USB uses NRZI line coding, which basically means that the data lines can switch states at the clock period, or some multiple of the clock period, with an upper limit that is determined by the specific speed of operation.

This results in an energy distribution that has the overall shape of the sinc function (sin(x)/x). The main peak occurs at half the clock frequency, and there are "nulls" (frequencies of little to no energy) on either side of this peak. With NRZI, the first nulls occur at DC and at the clock frequency.

If you can transmit all of this frequency-domain "main lobe" to a receiver, you will have little trouble recovering the data from the signal, even though there will be some visible distortion of the actual time-domain waveform. If you try to reduce the bandwidth below this value, you will start to see significant amounts of ISI (intersymbol interference). Therefore, most people would say that the bandwidth of this type of signal is equal to the clock frequency.