Change your variable tax to double
double tax = 0;
Working Code,
Console.Write("Input money : ");
float money = Console.Read();
double tax = 0;
if (money < 10000)
{
tax = .05 * money;
}
else if (money <= 100000)
{
tax = .08 * money;
}
else
{
tax = .085 * money;
}
Console.WriteLine("Tax is {0}", tax);
Console.ReadLine();