Unless you practice saving your receipts after every single transaction, then you are not ready to budget. Once you track your receipts by taking them home, sitting down to place the expense in your B.I.E., then and only then should you throw your receipt away. That is of course, unless you need to retain your receipt.
Never underestimate a receipt in a transaction, and always retain the power in a transaction by knowing what is happening with your money at all times. The math you use in your B.I.E. is the same math the banks should use, although they trick you into giving them money through fees.
If you do not know what a B.I.E. is yet, then educate yourself by clicking here.