Carriage inwards

Carriage Inward is a part of my inventory cost group it under the Purchase Cost in Trading account.  Entry :

Purchase A\C    Dr 90

Carriage Inward A\C Dr 10

To Cash / Vendor                  100

Rs.100 will be grouped under Purchase cost and will taken for inventory valuation

thanks for the reply Mr Sk and Abhishek, but i still have a doubt 

for example we buy A 10 items @ 3 = 30 and B , 10 items @ 4 = 40 , lets assume the delivery charge is 10

so i should record 

Purchase A  30

Purchase B  40

Delivery charge 10         

                              TO     Cash                           80

Suppose i sell 5 items of A for 5 each, so the sales is 5 X 5 = 25, so i record 

Cash 25          

              TO   Sales A            25

Now at the end of month i take inventory count, and i will find 5 items of A , that is 5 X 3 =15 and 10 items of B , that is 10 X 4=40

So i think my entries will be 

Cost of sales Item A 15

                                           TO   Purchase                               15

and

Inventory A     15

Invetory   B      40

                                TO     Purchase                   55

My question is what happens to the delivery charge of 10. Or should i distribute the delivery charge among the cost of items , because from my entries , i have Dr purchase of 80 and at end of month , i have cr purchase of only 70 . My question may seem a bit stupid and very basic, but i dont understand this concept , as im new to this field, pls help