In a statement issued in the name of second commissioner of taxation, Greg Farr, the ATO said the "business as usual" approach had been decided upon after preliminary discussions with Siebel.
"After preliminary discussions with Siebel, we do not anticipate any implications for our Siebel deployment in the short-term," Farr said.
"We have sought the views of industry analysts and, over the next few days, look forward to sitting down with Siebel to discuss any longer-term ramifications associated with the deal".
The ATO -- which is deploying Siebel software as part of its AU$450 million change program -- had yesterday said it was reviewing the ramifications of the deal.
Oracle this week said the planned purchase would give it a "major beachhead" against bitter rival SAP.