If your transaction appears to be higher, it means that the merchant has performed an authorisation check on your payment.
What is an authorisation hold?
In order to ensure that the payment will be honoured (i.e., to verify that the account has the necessary funds), the merchant performs an authorisation hold for an amount greater than the final amount of your purchase.
This authorisation is shown as a 'pending' transaction on your account before it is replaced by a transaction for the actual amount of your purchase.
The merchants who do this the most are gas stations, car rental companies and hotels.