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 $24.52   8.656%   $26.6425   $26.64   $26.65   $26.60  
  Purchase #2 $206.36   10.808%   $228.6634   $228.66   $228.65   $228.70  
  Purchase #3 $248.59   5.204%   $261.5266   $261.53   $261.55   $261.50  
  Purchase #4 $212.49   6.584%   $226.4803   $226.48   $226.50   $226.50  
  Purchase #5 $72.79   5.208%   $76.5809   $76.58   $76.60   $76.60  
  Purchase #6 $235.88   9.293%   $257.8003   $257.80   $257.80   $257.80  
  Purchase #7 $226.67   11.759%   $253.3241   $253.32   $253.30   $253.30  
  7 purchase totals = $1,227.30       $1,331.0181   $1,331.01   $1,331.05   $1,331.00