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system
is there a dollar amount that, when adding massachusetts sales tax, precisely equals $200?
user
don't worry about it.  the state doesn't care about rounding error.  all you need to do is say "we charge our prices with tax included" - you know, like carnivals and movie theaters.   then follow the procedures your state specifies for computing reportable tax.  quite likely it wants your pre-tax sales total for the reporting period. to get that, total up your gross sales that you collected, and divide by (1 + tax rate).  just like djclayworth says, except do it on total sales instead of per-item.  if you need to do the split per-transaction for quickbooks or something, that's annoying.  what quickbooks says will be pennies off the method i describe above.  the state don't care as long as it's just pennies, or in their favor.
assistant