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 $243.90   8.809%   $265.3852   $265.39   $265.40   $265.40  
  Purchase #2 $183.70   9.452%   $201.0633   $201.06   $201.05   $201.10  
  Purchase #3 $67.61   13.475%   $76.7204   $76.72   $76.70   $76.70  
  Purchase #4 $20.62   11.659%   $23.0241   $23.02   $23.00   $23.00  
  Purchase #5 $62.66   8.580%   $68.0362   $68.04   $68.05   $68.00  
  Purchase #6 $45.57   11.815%   $50.9541   $50.95   $50.95   $51.00  
  Purchase #7 $248.27   5.120%   $260.9814   $260.98   $261.00   $261.00  
  7 purchase totals = $872.33       $946.1647   $946.16   $946.15   $946.20