How to display output with two digits of precision

Here is my code

class Atm

  attr_accessor :amount, :rem, :balance

  TAX = 0.50

  def transaction

    @rem = @balance=2000.00
    @amount = gets.chomp.to_f

    if @amount%5 != 0 || @balance < @amount
      "Incorrect Withdrawal Amount(not multiple of 5) or you don't have enough balance"
    else
      @rem = @balance-(@amount+TAX)
      "Successful Transaction"
    end
  end
end

a=Atm.new
puts "Enter amount for transaction"
puts a.transaction
puts "Your balance is #{a.rem.to_f}"

and my output is

Enter amount for transaction
100                              # user enters this value
Successful Transaction
Your balance is 1899.5

as you can see the output, 'Your balance is 1899.5' only displays one digit of precision. I need help to understand and fix the issue. I want two digits of precision in the output.

And also how can I improve this code?