Several khipus - Inka knotted-string recording devices - were recently excavated at a storage facility at the Peruvian south coast site of Inkawasi, found buried under agricultural produce (i.e., chili peppers, peanuts, and black beans). These khipus contain a formulaic arrangement of numerical values not encountered on khipus from elsewhere in Tawantinsuyu (the Inka Empire). The formula includes first, a large number, hypothesized to record the sum total of produce included in a deposit, followed by a fixed number, and then one or more additional numbers. The fixed number plus the additional number(s) sum to the original large number. It is hypothesized that the fixed number represents an amount deducted from the deposit to support storage facility personnel. As such, it represented a tax assessed on deposits, the first evidence we have for a system of taxation on goods in the Inka Empire. It is proposed that the size and complexity of the storage facility at Inkawasi prompted the invention of a kind of financing instrument - taxation - not known previously from Inka administration. We also consider, but provisionally set aside, the alternative hypothesis that the fixed values recorded on the Inkawasi khipus could have represented amounts of seeds set aside from deposits for the next year's planting.