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 $102.36   10.648%   $113.2593   $113.26   $113.25   $113.30  
  Purchase #2 $97.78   8.299%   $105.8948   $105.89   $105.90   $105.90  
  Purchase #3 $56.57   12.413%   $63.592   $63.59   $63.60   $63.60  
  Purchase #4 $201.45   12.318%   $226.2646   $226.26   $226.25   $226.30  
  Purchase #5 $206.70   11.119%   $229.683   $229.68   $229.70   $229.70  
  Purchase #6 $68.65   5.844%   $72.6619   $72.66   $72.65   $72.70  
  Purchase #7 $132.76   9.137%   $144.8903   $144.89   $144.90   $144.90  
  7 purchase totals = $866.27       $956.2459   $956.23   $956.25   $956.40