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 $56.47   12.751%   $63.6705   $63.67   $63.65   $63.70  
  Purchase #2 $42.53   4.357%   $44.383   $44.38   $44.40   $44.40  
  Purchase #3 $226.36   11.797%   $253.0637   $253.06   $253.05   $253.10  
  Purchase #4 $42.92   11.732%   $47.9554   $47.96   $47.95   $48.00  
  Purchase #5 $69.39   10.539%   $76.703   $76.70   $76.70   $76.70  
  Purchase #6 $225.36   8.689%   $244.9415   $244.94   $244.95   $244.90  
  Purchase #7 $140.99   8.296%   $152.6865   $152.69   $152.70   $152.70  
  7 purchase totals = $804.02       $883.4036   $883.40   $883.40   $883.50