If you were going to do this in a tag change event then you could use this script. Note this script will work in Version 7 or 8. For Version 7 you would need to change from system.tag.*Blocking() to system.tag.*All().
import struct
#read all tag values needed.
qValues = system.tag.readBlocking(['path/to/tag1','path/to/tag2','path/to/tag3','path/to/tag4','path/to/tag5'])
#convert to Ascii string
strVal = ''.join([struct.pack(qValue.value) for qValue in qValues])
#write value to new holding tag
system.tag.writeBlocking(['path/to/strTag'],[strVal])
You could do this in an expression to, though I haven't worked that out. You could use the expression from this post for some inspiration, it isn't exactly the same but it does take care of the conversion and concatenation. I think I prefer the script in this case.