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 $107.72   13.783%   $122.567   $122.57   $122.55   $122.60  
  Purchase #2 $45.81   4.232%   $47.7487   $47.75   $47.75   $47.70  
  Purchase #3 $154.29   11.290%   $171.7093   $171.71   $171.70   $171.70  
  Purchase #4 $98.31   9.462%   $107.6121   $107.61   $107.60   $107.60  
  Purchase #5 $73.96   10.307%   $81.5831   $81.58   $81.60   $81.60  
  Purchase #6 $25.32   6.177%   $26.884   $26.88   $26.90   $26.90  
  Purchase #7 $128.60   13.455%   $145.9031   $145.90   $145.90   $145.90  
  7 purchase totals = $634.01       $704.0073   $704.00   $704.00   $704.00