Solution for the freeCodCamp project "Cash Register" https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/javascript-algorithms-and-data-structures-projects/cash-register

cash-register.js

const unitValue = [
  ["PENNY", 0.01],
  ["NICKEL", 0.05],
  ["DIME", 0.1],
  ["QUARTER", 0.25],
  ["ONE", 1],
  ["FIVE", 5],
  ["TEN", 10],
  ["TWENTY", 20],
  ["ONE HUNDRED", 100]
]

/* Convert cidArray to object
 * Example for const unitValue 
{ 
  'ONE HUNDRED': 100,
  TWENTY: 20,
  TEN: 10,
  FIVE: 5,
  ONE: 1,
  QUARTER: 0.25,
  DIME: 0.1,
  NICKEL: 0.05,
  PENNY: 0.01 
}
 */ 
const cidToObj = cidArray => {
  let obj = {}
  let copiedArray = [...cidArray] // avoid the original array changed
  copiedArray.reverse().forEach( item => {
    obj[item[0]] = item[1]
  })
  return obj
}

/* 
 * Main function
 */
function checkCashRegister(price, cash, cid) {
  // Convert current cid and unitValue to object
  // Make them easy to access
  const cidObj = cidToObj(cid);
  const unitValueObj = cidToObj(unitValue)

  // Prepare values before running the loop 
  let res = { status: '', change: []}  
  let updatedCidObj = {}
  let updatedChange = cash - price

  // Lopp through all units
  for (let unit of Object.keys(cidObj) ) {
    let tempResAmount = Math.floor(updatedChange / unitValueObj[unit])
    let currentAmount = Math.round(cidObj[unit] / unitValueObj[unit])

    let resAmount = currentAmount <= tempResAmount ? currentAmount : tempResAmount;
    let resAmountValue = resAmount * unitValueObj[unit]
    
    updatedCidObj[unit] = parseFloat((cidObj[unit] - resAmountValue).toFixed(2))
    
    // Only push to res.change array if there is really an amount (>0)
    if ( resAmount > 0 ) {
      res.change.push([unit,resAmountValue])
      updatedChange = parseFloat((updatedChange - resAmountValue).toFixed(2))
    }

  }

  //Analyze and make the final decision for status and change
  if (updatedChange > 0) {
    res = {status: "INSUFFICIENT_FUNDS", change: []}
  }
  else if (Object.keys(updatedCidObj).every(unit => 0 === updatedCidObj[unit])) {
    // All units have 0 amount in updatedCidObj
    // That means no more money in drawer
    res = { status: 'CLOSED', change: cid}
  } 
  else {
    res.status = 'OPEN'
  }

  // Remove this comment in case want to check the result 
  // console.log(res)

  return res;
}

checkCashRegister(19.5, 500, [["PENNY", 400], ["NICKEL", ], ["DIME", 0], ["QUARTER", 0], ["ONE", 0], ["FIVE", 0], ["TEN", 0], ["TWENTY", 0], ["ONE HUNDRED", 800]]) 

// return
// { 
//  status: 'OPEN',
//  change: [ [ 'ONE HUNDRED', 400 ], [ 'NICKEL', 80.5 ] ] 
// }

Thank you!