Are "cause marketing" sales sales-taxable?

[TaxCPANY]

Client just threw me a curve:  some 'cause marketing' of their usual products -- i.e., they dedicated a few hours of an evening's sales to a charitable cause, didn't charge sales tax on those sales, and have told me this after-the-fact and a week before the quarter's return is due.  I can't find anything on-point on the state's tax website nor about reporting/accounting for this kind of sale.
My immediate concern is whether to include those sales among sales-taxable sales -- i.e., does the client 'eat' the sales tax that ordinarily would have been charged or are those sales  excluded?  I favor the former; the customers were not tax-exempt entities -- and it would be nigh impossible to document by now whether any of them were.  Or am I thinking too narrowly, rather puritanically about this?
Thank you in advance for any of your thoughts and/or references to previous discussions of or articles on this topic.

[ILLMAS]

The department of revenue doesn’t care who pays it, but when the end user is not tax exempt, somebody better come up with the sales tax amount.  

[schirallicpa]

When in doubt, pay up.  That's the NYS motto.