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 $59.45   6.774%   $63.4771   $63.48   $63.50   $63.50  
  Purchase #2 $183.87   5.542%   $194.0601   $194.06   $194.05   $194.10  
  Purchase #3 $22.54   13.791%   $25.6485   $25.65   $25.65   $25.60  
  Purchase #4 $50.93   4.247%   $53.093   $53.09   $53.10   $53.10  
  Purchase #5 $102.46   11.503%   $114.246   $114.25   $114.25   $114.20  
  Purchase #6 $247.95   4.146%   $258.23   $258.23   $258.25   $258.20  
  Purchase #7 $43.56   12.332%   $48.9318   $48.93   $48.95   $48.90  
  7 purchase totals = $710.76       $757.6865   $757.69   $757.75   $757.60