allow fractional feerates (#4324)

lib/simple_config.py

@@ -3,6 +3,7 @@ import threading
 import time
 import os
 import stat
+from decimal import Decimal
 
 from copy import deepcopy
 
@@ -473,12 +474,9 @@ class SimpleConfig(PrintError):
 
     @classmethod
     def estimate_fee_for_feerate(cls, fee_per_kb, size):
-        # note: We only allow integer sat/byte values atm.
-        # The GUI for simplicity reasons only displays integer sat/byte,
-        # and for the sake of consistency, we thus only use integer sat/byte in
-        # the backend too.
-        fee_per_byte = int(fee_per_kb / 1000)
-        return int(fee_per_byte * size)
+        fee_per_kb = Decimal(fee_per_kb)
+        fee_per_byte = fee_per_kb / 1000
+        return round(fee_per_byte * size)
 
     def update_fee_estimates(self, key, value):
         self.fee_estimates[key] = value