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   7.851%   $58.768   $58.77   $58.75   $58.80  
  Purchase #2 $224.27   6.519%   $238.8902   $238.89   $238.90   $238.90  
  Purchase #3 $183.46   8.217%   $198.5349   $198.53   $198.55   $198.50  
  Purchase #4 $63.54   4.412%   $66.3434   $66.34   $66.35   $66.30  
  Purchase #5 $66.92   10.149%   $73.7117   $73.71   $73.70   $73.70  
  Purchase #6 $35.78   12.344%   $40.1967   $40.20   $40.20   $40.20  
  Purchase #7 $113.99   7.538%   $122.5826   $122.58   $122.60   $122.60  
  7 purchase totals = $742.45       $799.0275   $799.02   $799.05   $799.00