I want to add CESS charges to my sale vouchers but it is not showing. What should I do to add CESS?

If Cess is not being applied in a sale voucher in BUSY, then you need to make sure that Cess is enabled and the tax category within the item master is configured with Cess. Here are the steps you need to follow:
 Step 1: Go to the Administration menu.
 Step 2: Click on the Feature and Option tab.
 Step 3: Click on the GST/VAT button and enable Cess from there.
 Step 4: After enabling Cess, you need to create a Tax category with Cess configuration in it.
 Step 5: To create a tax category master, click on the Administration menu, then click on the master, then click on the tax category master, and define the name as Tax rate name with Cess percentage. Then define the tax rate. Next to it, there will be an option to specify Cess rate. Select Y in front of it, then define the rate and its basis.
 Step 6: You need to define that new tax category within all those items in which you want to use it.
 Step 7: Now in the voucher, if you take purchase/sale type as Local/Central item wise, after applying the item name in the item body, Cess will automatically apply along with tax when you will click on the amount column.
 Step 8: But if you use Multi rate or other types in which you define tax rate in bill sundry, then after defining the item name in the body, when you will click on the apply tax option or press F2, then F4 then Cess will apply in bill sundry along with tax.