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 $60.83   7.319%   $65.2821   $65.28   $65.30   $65.30  
  Purchase #2 $135.78   12.393%   $152.6072   $152.61   $152.60   $152.60  
  Purchase #3 $166.70   5.412%   $175.7218   $175.72   $175.70   $175.70  
  Purchase #4 $175.49   13.730%   $199.5848   $199.58   $199.60   $199.60  
  Purchase #5 $110.75   11.189%   $123.1418   $123.14   $123.15   $123.10  
  Purchase #6 $25.94   5.514%   $27.3703   $27.37   $27.35   $27.40  
  Purchase #7 $217.32   11.661%   $242.6617   $242.66   $242.65   $242.70  
  7 purchase totals = $892.81       $986.3697   $986.36   $986.35   $986.40