If you use more than the inclusive 5GB on your standard rate price plan, you will simply be charged for any additional bandwidth that you use. Bandwidth is charged incrementally, so if you use 5.1GB, you just pay for the extra 0.1GB.
You can easily monitor your bandwidth usage in real time from within your account.
If you are regularly using more than the inclusive bandwidth, please note that we now offer a range of price plans to best suit your needs. These can be viewed here.