Three sets of toy organizers cost $78 x 3 = $<<78*3=234>>234.
Two gaming chairs cost $83 x 2 = $<<83*2=166>>166
Leon's total orders amount to $234 + $166 = $<<234+166=400>>400.
Then, the delivery fee is $400 x 5/100 = $<<400*5/100=20>>20.
So, Leon had to pay a total of $400 + $20 = $<<400+20=420>>420.
#### 420