As per accounting standard 2 issued by ICAI, inventories are valued at cost or market price whichever is lower.
Cost is determined based on few methods such as FIFO, Weighted average, etc., as said in AS 2.
Tally has the option of chosing the method in which the stock is to be valued. If the input is correct, both the valuation (as per tally or any other mode) should tie up.
In addition to compliance with AS-2 to be ensured as mentioned by Dinesh, please check how costs of both - WIP and finished goods have been arrived at, viz., what overheads and in what ratios have been added and whether the proportion is reasonable as per your understanding of business of the client and as per the last year valuation made. Also, consult a senior team member of your audit team who has done this in the previous year.