15 June 2010
I think there is not a big issue in this. You can bill with the same amount or round off amount. In case, there is difference in recording by you and your sister concern, then later on at at year end, there might be minor difference which can be sett off and also can be shown as miscellaneous income/miscellaneous expenses. Also, consider the payments made/received because it will be required to make you to adjust the payment made/received against bill recived/issued.
So to avoid any reconciliation at the year end, try to use any one of the method both by you and your sister concern.