Finding places to "split" the journey into a combination of tickets:
Use a WebTIS website (e.g. EC, LM etc) and click the info (i) button next to the itinerary you want, then tick 'show all calling points', this shows the places where you could "split" the journey into a combination of tickets (note the train must call on the return journey too).
If you are returning (you have not stated if you are or not) then note that if you want to return a different day, then unless singles are sensibly priced (unlikely in the case of shorter distance singles) it will not be cheaper to split at stations where only Off Peak / Anytime Day Return tickets are available. Therefore, you can generally only look at longer distance tickets (where SVRs exist) to combine.
"Splitting" isn't the only way to reduce the cost. You can look at Routeing Guide anomalies by looking for 'over-distance' tickets which you can then start/finish short, though ATOC and some TOCs are keen to remove such anomalies so if they get mentioned here that can mean the end of them.
Travelling at "peak" times can be reduced by purchasing tickets with more favourable restrictions and either splitting and/or starting/finishing short. Again, some TOCs do not like this and can take action to change these restrictions on some flows.
The fares for Sheffield-Halifax (avoiding Doncaster) are:
Anytime Day Single £12-10
Off Peak Day Return £12-50
Anytime Day Return £15-10
Anytime Return £16-00
