Returns the number rounded to the nearest interval - use `Math.round` if you need upper rounding.

rounded.js

const levels = [
    [1001, 1],[1000.5, 1],[1000, 1]
]

/**
 * Returns the number rounded to the nearest interval.
 * Example:
 * 
 *   roundToNearest(80, 100); // 100
 *   roundToNearest(25, 15);  // 30
 * 
 * @param {number} value    The number to round
 * @param {number} interval The numeric interval to round to
 * @return {number}
 */
 function roundToNearest(value, interval) {
    // return Math.round(value/interval) * interval;
    return Math.floor(value/interval) * interval;
  }

console.log(roundToNearest(1000.5, 1))