Fix and improve Tick size ROUND_DOWN logic

freqtrade/exchange/exchange_utils.py

@@ -279,15 +279,15 @@ def price_to_precision(
                                               ))
 
         if precisionMode == TICK_SIZE:
-            if rounding_mode == ROUND:
-                ticks = price / price_precision
-                rounded_ticks = round(ticks)
-                return rounded_ticks * price_precision
             precision = FtPrecise(price_precision)
             price_str = FtPrecise(price)
             missing = price_str % precision
             if not missing == FtPrecise("0"):
-                return round(float(str(price_str - missing + precision)), 14)
+                if rounding_mode == ROUND_UP:
+                    res = price_str - missing + precision
+                elif rounding_mode == ROUND_DOWN:
+                    res = price_str - missing
+                return round(float(str(res)), 14)
             return price
         elif precisionMode in (SIGNIFICANT_DIGITS, DECIMAL_PLACES):
 

tests/exchange/test_exchange_utils.py

@@ -247,11 +247,14 @@ def test_amount_to_precision(amount, precision_mode, precision, expected,):
     (2.34559, TICK_SIZE, 0.001, 2.346, ROUND_UP),
     (2.9999, TICK_SIZE, 0.001, 3.000, ROUND_UP),
     (2.9909, TICK_SIZE, 0.001, 2.991, ROUND_UP),
+    (2.9909, TICK_SIZE, 0.001, 2.990, ROUND_DOWN),
     (2.9909, TICK_SIZE, 0.005, 2.995, ROUND_UP),
     (2.9973, TICK_SIZE, 0.005, 3.0, ROUND_UP),
     (2.9977, TICK_SIZE, 0.005, 3.0, ROUND_UP),
     (234.43, TICK_SIZE, 0.5, 234.5, ROUND_UP),
+    (234.43, TICK_SIZE, 0.5, 234.0, ROUND_DOWN),
     (234.53, TICK_SIZE, 0.5, 235.0, ROUND_UP),
+    (234.53, TICK_SIZE, 0.5, 234.5, ROUND_DOWN),
     (0.891534, TICK_SIZE, 0.0001, 0.8916, ROUND_UP),
     (64968.89, TICK_SIZE, 0.01, 64968.89, ROUND_UP),
     (0.000000003483, TICK_SIZE, 1e-12, 0.000000003483, ROUND_UP),