What is the right way to show additional charges like cleaning, folding etc on invoices?

You can show additional charges as a item or as a bill sundry
To show additional charges as item follow below mentioned steps:
Step 1: Go to administration menu
Step 2: Then click on masters option and click on item then click on add option
Step 3: Then add a item specify name and select unit as NA 
Step 4: Set do not maintain stock balance option as yes in item master and save it
Step 5: Then go to transactions tab and you can select an invoice and you can use the additional charges as an item
To show additional charges as bill sundry follow these steps:
Step 1: Go to administration menu
Step 2: Then click on masters option
Step 3: Then click on bill sundry 
Step 4: Then click on add option and you can create bill sundry and it will be treated as additional charges
step 5: Then click on add option then specify bill sundry name 
Step 6: Make sure to select bill sundry type as addictive
Step 7: You can select bill sundry as percentage base,per quantity base and as absolute amount
Step 8: Then go to transaction tab and create a invoice and you can use that bill sundry as a additional charges