No. According to both the DMG(3.5e) and the MM the CR corresponds to a party of equal level. That is to say, a CR-5 creature/encounter should be a moderate challenge for a party of four 5th-level characters. Assuming the characters are fresh going into the battle and come out the other side a bit battered. XP awards are adjusted by the difference between the party's level and the CR of the creature/encounter. (See table 2-6 of the DMG(3.5e). By this table your 10th-level party would receive 500 xp for a CR-5 encounter where the 5th-level party would receive 1,500 XP.)
Things to remember:
- Essentially the CR has a direct relationship to the level of the party as a whole, not any individual character.
- The CR is based on a four-member party. The CR needs to be adjusted for parties of varied size.
- The CR assumes that the party is in top shape and not yet worn down by previous battles.