Ken,
Just scan for both. I don't know about where you are located, but looking at radioreference.com for my area, the use of the older CTCSS is still more likely to be used than DCS. There are also fewer CTCSS tones to scan than DCS codes. So I would start by scanning CTCSS. If the odds are in your favor and it is found to be CTCSS, you won't have to scan DCS at all.

Also remember that if you are trying to find the tone/code to access a repeater, you have to listen/scan the frequency that the repeater users transmit on to determine the tone/code. In this case I would do the scanning in VFO/frequency mode listening to the frequency I would normally transmit on.

Jim KC9HI