@CommunityPool You could sell them e-gift cards in any increment, which they could use to pay for items later.  These can be sold from your online store (if you have one), OR from your POS directly.  When selling these, you will be asked for a customer’s email address to send the e-gift card to.  They can then show this to your employees when they buy something, so that your employees can key in the gift card number and redeemed part of it.  Customers can even reload their gift card when it is running dry.  

Obviously these wouldn’t be “gifts” to other people, but customers buying them for themselves.  But I think it would have the effect you want.

Would that work for you?  Here’s lots of information about these.

https://squareup.com/help/us/en/article/6000-square-egift-cards

One caution. Every state handles the legalities of pre-paying (gift cards or otherwise) differently.  In some states, business must claim the income immediately on the purchase of a gift card.  In others, you claim the income as the card is redeemed.  And sales taxes have to be charged to someone — either the gift card purchaser or the person who redeems the gift card.  And then there is the problem of when you have to unused gift card funds as income.  So check with your accountant about what you need to do in your state.  A lot depends on the account method you use — cash or accrual.

Best,