input: Write a python function to calculate the total cost including tax, ensuring the result is rounded to the nearest hundredth.
  assert calculate_tax(100, 0.07) == 107.00
  assert calculate_tax(59.99, 0.08) == 64.79
  assert calculate_tax(200, 0.075) == 215.00
output: def calculate_tax(price, tax_rate):
      total_cost = price * (1 + tax_rate)
      return round(total_cost, 2)