Delivery cost is not equal to actual cost in sales order

I met a strange phenomenon is the sale cost in SO is not equal to the cost in delivery order.

I order 3 PCS material and each cost is 43.87 and the total cost is 131.61.

However when I finished PGI the FI document shows the cost is 131.62. the diff is 0.01

I don't know how the diff comes.

Do you know the reason for the above issue?

Thank you very much for your help.

Yang