Are sales considered a less stable career?

If there is a sales tax, which depends on the sales sum, how should the sales be aggregated when generating an invoice for a 3-month period?

• If there is a http://www.nyc.gov/html/dof/html/business/nys_sales_tax.shtml (5% if less than $100, 3% if more than $100), how should the sales be aggregated when generating an invoice for 3 months period? Should the sales tax be considered per each month, or it should be calculated for overall invoice sales sum?

• Answer:

  Sales tax is a percentage of the sales amount, so if it is 7%, that is 7 cents on each dollar and it would be aggregated proportionally. $100 in sales + $7 in tax, $200 in sales + $14.00 in tax, etc. is how you would invoice it.