Rounding with PRBMath

PRBMathRounding.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import {UD60x18} from "@prb/math/UD60x18.sol";
import {SD59x18} from "@prb/math/SD59x18.sol";

library PRBMathRounding {
  SD59x18 constant iONE = SD59x18.wrap(1e18);
  SD59x18 constant iTEN = SD59x18.wrap(10e18);
  UD60x18 constant ONE_THOUSAND = UD60x18.wrap(1000e18);
  
  /// @notice Rounds `n` to the `d` digit from the highest digit
  ///         https://www.desmos.com/calculator/bhbzwyrkjm
  /// @param n The number to round (18 decimals)
  /// @param d The number of digits from the highest digit (18 decimals)
  function roundTo(UD60x18 n, UD60x18 d) internal pure returns (UD60x18) {
    SD59x18 v = n.intoSD59x18().log10().sub(d).floor();
    SD59x18 r = n.intoSD59x18().div(iTEN.pow(v));
    r = r.frac() < iONE_HALF ? r.floor() : r.ceil();
    UD60x18 s = r.mul(iTEN.pow(v)).intoUD60x18();
    return n < ONE_THOUSAND ? s : s.ceil();
  }
}