input: Write a function to optimize the given Python code snippet for determining commission rates based on gross sales. The function should return the correct commission rate as specified in the original code but should be more efficient.
  assert determine_commission_rate(12000)==0.1
  assert determine_commission_rate(7500)==0.07
  assert determine_commission_rate(2500)==0.05
  assert determine_commission_rate(10000)==0.1
  assert determine_commission_rate(4999)==0.05
output: def determine_commission_rate(gross_sales):
      if gross_sales >= 10000:
          return 0.1
      elif gross_sales >= 5000:
          return 0.07
      else:
          return 0.05