Intendi in questo modo ?
codice:
const TRIBUTO1 = 1
const TRIBUTO2 = 2
const TRIBUTO4 = 4

const pagato = [
    { tot: 10, tributo: TRIBUTO1 },
    { tot: 4, tributo: TRIBUTO2 }
]
const non_pagato = [
    { tot: 10, tributo: TRIBUTO2 },
    { tot: 3, tributo: TRIBUTO4 }
]
const non_pagabile = []

const joinData = [...pagato, ...non_pagato, ...non_pagabile]
// labels
const labels = [...new Set(joinData.map(obj => obj['tributo']))]
//total
const total = joinData.reduce((sum, obj) => {
    return sum + obj['tot']
}, 0)

console.log(`labels: ${labels}`)
console.log(`total: ${total}`)