Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $77.96   11.116%   $86.626   $86.63   $86.65   $86.60  
  Purchase #2 $79.56   10.824%   $88.1716   $88.17   $88.15   $88.20  
  Purchase #3 $157.59   10.695%   $174.4443   $174.44   $174.45   $174.40  
  Purchase #4 $76.74   6.862%   $82.0059   $82.01   $82.00   $82.00  
  Purchase #5 $240.57   8.626%   $261.3216   $261.32   $261.30   $261.30  
  Purchase #6 $7.79   6.256%   $8.2773   $8.28   $8.30   $8.30  
  Purchase #7 $15.44   3.326%   $15.9535   $15.95   $15.95   $16.00  
  7 purchase totals = $655.65       $716.8002   $716.80   $716.80   $716.80