See enclosed link which will be of use to you. Although not my area of expertise, I believe sales tax is a no-no to add to the cost BUT bottle deposits are appropriate.
My answer is not intended to be giving legal advice and this topic can be a complex area where the advice of a licensed attorney in your State should be obtained.
You cannot charge State or local sales taxes on eligible items
purchased with SNAP benefits. You may not include the
sales tax in the purchase price as a hidden cost. Keeping
eligible and ineligible items separate if you do not have
electronic cash registers and scanners will also prevent you
from accidentally charging sales tax on eligible items. If you
have questions about your State’s sales tax laws, you should
contact your State tax department.
SNAP benefits can cover the entire cost of items such as
eligible drinks in returnable bottles where the price includes a
specific bottle deposit. This is true even if the deposit is not
included in the shelf price.