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 $233.52   11.208%   $259.6929   $259.69   $259.70   $259.70  
  Purchase #2 $74.99   6.163%   $79.6116   $79.61   $79.60   $79.60  
  Purchase #3 $119.40   11.671%   $133.3352   $133.34   $133.35   $133.30  
  Purchase #4 $58.31   6.613%   $62.166   $62.17   $62.15   $62.20  
  Purchase #5 $136.43   13.544%   $154.9081   $154.91   $154.90   $154.90  
  Purchase #6 $222.41   6.403%   $236.6509   $236.65   $236.65   $236.70  
  Purchase #7 $32.32   8.617%   $35.105   $35.11   $35.10   $35.10  
  7 purchase totals = $877.38       $961.4697   $961.48   $961.45   $961.50