It’s about the usage of the function round.

#include <bits/stdc++.h>

using namespace std;

// Complete the solve function below.
void solve(double meal_cost, int tip_percent, int tax_percent) {

    cout << round(meal_cost * (1 + double(tip_percent + tax_percent) / 100)) << endl;
}

int main()
{
    double meal_cost;
    cin >> meal_cost;
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

    int tip_percent;
    cin >> tip_percent;
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

    int tax_percent;
    cin >> tax_percent;
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

    solve(meal_cost, tip_percent, tax_percent);

    return 0;
}

References

1. http://www.cplusplus.com/reference/cmath/round/