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 $47.99   9.537%   $52.5668   $52.57   $52.55   $52.60  
  Purchase #2 $177.64   7.829%   $191.5474   $191.55   $191.55   $191.50  
  Purchase #3 $126.61   13.283%   $143.4276   $143.43   $143.45   $143.40  
  Purchase #4 $93.73   11.418%   $104.4321   $104.43   $104.45   $104.40  
  Purchase #5 $248.88   13.809%   $283.2478   $283.25   $283.25   $283.20  
  Purchase #6 $110.50   3.393%   $114.2493   $114.25   $114.25   $114.20  
  Purchase #7 $48.27   12.819%   $54.4577   $54.46   $54.45   $54.50  
  7 purchase totals = $853.62       $943.9287   $943.94   $943.95   $943.80