Fix layer canvas reuse

If the scale values have more than 6 decimals they are rounded and can no longer be
compared to the created transform string.

src/ol/transform.js

@@ -1,6 +1,7 @@
 /**
  * @module ol/transform
  */
+import {WORKER_OFFSCREEN_CANVAS} from './has.js';
 import {assert} from './asserts.js';
 
 /**
@@ -265,11 +266,24 @@ export function determinant(mat) {
 }
 
 /**
- * A string version of the transform.  This can be used
+ * @type {HTMLElement}
+ * @private
+ */
+let transformStringDiv;
+
+/**
+ * A rounded string version of the transform.  This can be used
  * for CSS transforms.
  * @param {!Transform} mat Matrix.
  * @return {string} The transform as a string.
  */
 export function toString(mat) {
-  return 'matrix(' + mat.join(', ') + ')';
+  const transformString = 'matrix(' + mat.join(', ') + ')';
+  if (WORKER_OFFSCREEN_CANVAS) {
+    return transformString;
+  }
+  const node =
+    transformStringDiv || (transformStringDiv = document.createElement('div'));
+  node.style.transform = transformString;
+  return node.style.transform;
 }