Gravity Forms v188.8.131.52 has been released via automatic update. If you are running older versions of Gravity Forms, including the initial v1.6.4 release, you should update to this new release. It resolves 2 issues that were discovered in the brand new Gravity Forms v1.6.4.
The second issue that has been patched is a calculation rounding issue when using the Product Field configured as a calculation. The price was being rounded to a whole number rather than rounding to 2 decimal places which is the appropriate format for rounding currency.
You can update to the latest version of Gravity Forms using Automatic Update. Just visit the Updates page under the Forms navigation in your WordPress Dashboard. Update deployment is staged so if you do not see the update available, try again in a few hours. You can also download the latest version of the plugin from the Downloads page.