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Why charge gross receipts taxes to the customer?
the state of New Mexico provides guidance in this exact situation. On page 4: Gross receipts DOES NOT include: Example: When the seller passes tax to the buyer, the seller should   separate, or “back out”, that tax from the total income to arrive at   "Gross Receipts," the amount reported in Column D of the CRS-1 Form.   (Please see the example on page 48.) and on page 48: How do I separate (“back out”) gross receipts tax from total gross receipts?  See the following examples of how to separate the gross   receipts tax:  1) To separate (back out) tax from total receipts at the   end of the report period, first subtract deductible and exempt   receipts, and then divide total receipts including the tax for the   report period by one plus the applicable gross receipts tax rate.  For example, if your tax rate is 5.5% and your total receipts    including tax are $1,055.00 with no deductions or exemptions, divide   $1,055.00 by 1.055. The result is your gross receipts excluding tax   (to enter in Column D of the CRS-1 Form) or $1,000.  2) If your tax   rate is 5.5%, and your total gross receipts including tax are   $1,055.00, and included in that figure are $60 in deductions and   another $45 in exemptions:  a) Subtract $105 (the sum of your   deductions and exemptions) from $1,055. The remainder is $950. This   figure still includes the tax you have recovered from your buyers.  b) Divide $950 by 1.055 (1 plus the 5.5% tax rate). The result is   $900.47.  c) In Column D enter the sum of $900.47 plus $60 (the amount   of deductible receipts)*, or $960.47. This figure is your gross   receipts excluding tax.