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 $232.76   11.691%   $259.972   $259.97   $259.95   $260.00  
  Purchase #2 $92.41   5.602%   $97.5868   $97.59   $97.60   $97.60  
  Purchase #3 $112.46   12.347%   $126.3454   $126.35   $126.35   $126.30  
  Purchase #4 $161.86   13.518%   $183.7402   $183.74   $183.75   $183.70  
  Purchase #5 $90.26   5.217%   $94.9689   $94.97   $94.95   $95.00  
  Purchase #6 $35.57   13.269%   $40.2898   $40.29   $40.30   $40.30  
  Purchase #7 $92.72   10.850%   $102.7801   $102.78   $102.80   $102.80  
  7 purchase totals = $818.04       $905.6832   $905.69   $905.70   $905.70