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 $245.73   6.291%   $261.1889   $261.19   $261.20   $261.20  
  Purchase #2 $156.90   8.124%   $169.6466   $169.65   $169.65   $169.60  
  Purchase #3 $26.88   11.795%   $30.0505   $30.05   $30.05   $30.10  
  Purchase #4 $152.81   5.116%   $160.6278   $160.63   $160.65   $160.60  
  Purchase #5 $128.80   6.775%   $137.5262   $137.53   $137.55   $137.50  
  Purchase #6 $65.34   3.869%   $67.868   $67.87   $67.85   $67.90  
  Purchase #7 $138.69   12.250%   $155.6795   $155.68   $155.70   $155.70  
  7 purchase totals = $915.15       $982.5875   $982.60   $982.65   $982.60