Nested conditional - trade commission

#include <iostream>
#include<string>
using namespace std;
int main()
{
    string town;
    cin >> town;
    double sells;
    cin >> sells;
    double commissions = -1.0;



    if (town == "Sofia") {
        if (sells >= 0 && sells <= 500) {
            commissions = sells * 0.05;
        }
        else if (sells> 500 && sells <= 1000) {
            commissions = sells * 0.07;
        }
        else if (sells > 1000 && sells <= 10000) {
            commissions = sells *0.08;
        }
        else if (sells > 10000) {
            commissions = sells * 0.12;
        }
    }
    else if (town == "Varna") {
        if (sells >= 0 && sells <= 500) {
            commissions = sells * 0.045;
        }
        else if (sells > 500 && sells <= 1000) {
            commissions = sells * 0.075;
        }
        else if (sells > 1000 && sells <= 10000) {
            commissions = sells * 0.1;
        }
        else if (sells > 10000) {
            commissions = sells * 0.13;
        }
    }
    else if (town == "Plovdiv") {
        if (sells >= 0 && sells <= 500) {
            commissions = sells * 0.055;
        }
        else if (sells > 500 && sells <= 1000) {
            commissions = sells * 0.08;
        }
        else if (sells > 1000 && sells <= 10000) {
            commissions = sells * 0.12;
        }
        else if (sells > 10000) {
            commissions = sells * 0.145;
        }
        if( sells > 0 || town == "valid ")
        {

        cout.setf(ios::fixed);
        cout.precision(2);
        cout << commissions << endl;
        }
        else
            cout << "error" << endl;
    }
    return 0;
}