Rounding Values in a Formula Field

I have a custom object with a custom currency field called Revenue__c where users enter the exact dollar amount (i.e. $23,187,098.88). I trying to create a formula field called Rev__c that I will display the values from the Revenue__c field rounded to a specified number.

For Example:
IF (Revenue__c) = $23,187,098.88 THEN (Rev__c) = "$23.2M" - nearest 100,000

IF (Revenue__c) = $3,187,098.88 THEN (Rev__c) = "$3.2M" - nearest 100,000

IF (Revenue__c) = $318,700 THEN (Rev__c) = "$0.32M" - nearest 10,000

IF (Revenue__c) = $87,098 THEN (Rev__c) = "$0.087M" - nearest 1,000