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 $95.41   8.364%   $103.3901   $103.39   $103.40   $103.40  
  Purchase #2 $130.56   6.230%   $138.6939   $138.69   $138.70   $138.70  
  Purchase #3 $63.44   9.577%   $69.5156   $69.52   $69.50   $69.50  
  Purchase #4 $6.91   4.583%   $7.2267   $7.23   $7.25   $7.20  
  Purchase #5 $131.94   10.606%   $145.9336   $145.93   $145.95   $145.90  
  Purchase #6 $23.89   11.740%   $26.6947   $26.69   $26.70   $26.70  
  Purchase #7 $247.34   5.786%   $261.6511   $261.65   $261.65   $261.70  
  7 purchase totals = $699.49       $753.1057   $753.10   $753.15   $753.10