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 $241.33   7.459%   $259.3308   $259.33   $259.35   $259.30  
  Purchase #2 $46.79   13.506%   $53.1095   $53.11   $53.10   $53.10  
  Purchase #3 $207.28   10.289%   $228.607   $228.61   $228.60   $228.60  
  Purchase #4 $142.55   8.457%   $154.6055   $154.61   $154.60   $154.60  
  Purchase #5 $103.58   10.424%   $114.3772   $114.38   $114.40   $114.40  
  Purchase #6 $43.63   8.595%   $47.38   $47.38   $47.40   $47.40  
  Purchase #7 $62.53   7.708%   $67.3498   $67.35   $67.35   $67.30  
  7 purchase totals = $847.69       $924.7598   $924.77   $924.80   $924.70