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 $54.49   3.785%   $56.5524   $56.55   $56.55   $56.60  
  Purchase #2 $124.95   9.456%   $136.7653   $136.77   $136.75   $136.80  
  Purchase #3 $163.45   3.822%   $169.6971   $169.70   $169.70   $169.70  
  Purchase #4 $227.68   5.189%   $239.4943   $239.49   $239.50   $239.50  
  Purchase #5 $7.38   4.206%   $7.6904   $7.69   $7.70   $7.70  
  Purchase #6 $167.88   7.283%   $180.1067   $180.11   $180.10   $180.10  
  Purchase #7 $8.76   9.158%   $9.5622   $9.56   $9.55   $9.60  
  7 purchase totals = $754.59       $799.8684   $799.87   $799.85   $800.00