GnuCash doesn't handle fractional cents properly with tax tables

[Omari Stephens]

Howdy, y'all.  I'm pretty sure there's a bug here, but it's not clear to 
me yet whether I'm also doing something wrong, or whether this just 
needs to be fixed.

My total sales tax rate is 8.5%.  So I charge 8.5% on top of the 
subtotal.  My sales tax rate consists of a city rate of 0.25%, a county 
rate of 2.25%, and a state rate of 6.0%.

I recently sent a $150 invoice to a customer through PayPal, which just 
charges the final rate of 8.5%.  So the total invoice amount was $150 + 
$12.75 == $162.75

When I try to enter the invoice in GnuCash, with "Taxable?" checked and 
"Tax included?" _not_ checked for a $150.00 line, it shows the figured 
tax amount as $12.7_6_.  Presumably related to the fact that the city 
tax amount is $0.375 and the county tax amount is $3.375 .  I could see 
this as being a confusing non-bug.

However, when I try to enter a $162.75 line with "Taxable?" checked and 
"Tax included?" _also_ checked, it back-calculates a $150.00 subtotal, 
and again shows a $12.76 tax amount.  The big problem is that this still 
results in a total invoice amount of $162.7_6_, which is wrong and 
doesn't match what I entered.  It's clearly a bug that when I enter a 
$162.75 line with tax included, my total invoice amount ends up at $162.76.

FWIW, my currency is USD, I have three collected-tax accounts, and I've 
tried setting the "Smallest fraction" for those accounts to "1/1000", 
which seems like it theoretically should accommodate the half-cents that 
are required to resolve this linear equation.

Thoughts?  Suggestions?  I'll probably just record a 1-cent correction 
line for now, but this is kind of frustrating.  This is GnuCash 2.6.15.

--Omari