diff --git a/base/src/functions/mathematical.rs b/base/src/functions/mathematical.rs
index 8931b58..4f9cc88 100644
--- a/base/src/functions/mathematical.rs
+++ b/base/src/functions/mathematical.rs
@@ -2,6 +2,7 @@ use crate::cast::NumberOrArray;
 use crate::constants::{LAST_COLUMN, LAST_ROW};
 use crate::expressions::parser::ArrayNode;
 use crate::expressions::types::CellReferenceIndex;
+use crate::number_format::to_precision;
 use crate::single_number_fn;
 use crate::{
     calc_result::CalcResult, expressions::parser::Node, expressions::token::Error, model::Model,
@@ -311,7 +312,7 @@ impl Model {
             return CalcResult::new_args_number_error(cell);
         }
         let value = match self.get_number(&args[0], cell) {
-            Ok(f) => f,
+            Ok(f) => to_precision(f, 15),
             Err(s) => return s,
         };
         let number_of_digits = match self.get_number(&args[1], cell) {
@@ -327,12 +328,13 @@ impl Model {
         let scale = 10.0_f64.powf(number_of_digits);
         CalcResult::Number((value * scale).round() / scale)
     }
+
     pub(crate) fn fn_roundup(&mut self, args: &[Node], cell: CellReferenceIndex) -> CalcResult {
         if args.len() != 2 {
             return CalcResult::new_args_number_error(cell);
         }
         let value = match self.get_number(&args[0], cell) {
-            Ok(f) => f,
+            Ok(f) => to_precision(f, 15),
             Err(s) => return s,
         };
         let number_of_digits = match self.get_number(&args[1], cell) {
@@ -352,12 +354,13 @@ impl Model {
             CalcResult::Number((value * scale).floor() / scale)
         }
     }
+
     pub(crate) fn fn_rounddown(&mut self, args: &[Node], cell: CellReferenceIndex) -> CalcResult {
         if args.len() != 2 {
             return CalcResult::new_args_number_error(cell);
         }
         let value = match self.get_number(&args[0], cell) {
-            Ok(f) => f,
+            Ok(f) => to_precision(f, 15),
             Err(s) => return s,
         };
         let number_of_digits = match self.get_number(&args[1], cell) {
diff --git a/base/src/test/mod.rs b/base/src/test/mod.rs
index a0a0d69..4fab1c2 100644
--- a/base/src/test/mod.rs
+++ b/base/src/test/mod.rs
@@ -55,6 +55,7 @@ mod test_arrays;
 mod test_escape_quotes;
 mod test_extend;
 mod test_fn_fv;
+mod test_fn_round;
 mod test_fn_type;
 mod test_frozen_rows_and_columns;
 mod test_geomean;
diff --git a/base/src/test/test_fn_round.rs b/base/src/test/test_fn_round.rs
new file mode 100644
index 0000000..a29d5d8
--- /dev/null
+++ b/base/src/test/test_fn_round.rs
@@ -0,0 +1,15 @@
+#![allow(clippy::unwrap_used)]
+
+use crate::test::util::new_empty_model;
+
+#[test]
+fn fn_round_approximation() {
+    let mut model = new_empty_model();
+    model._set("A1", "=ROUND(1.05*(0.0284+0.0046)-0.0284,4)");
+    model._set("A2", "=ROUNDDOWN(1.05*(0.0284+0.0046)-0.0284,5)");
+
+    model.evaluate();
+
+    assert_eq!(model._get_text("A1"), *"0.0063");
+    assert_eq!(model._get_text("A2"), *"0.00625");
+}
\ No newline at end of file