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 $81.79   13.618%   $92.9282   $92.93   $92.95   $92.90  
  Purchase #2 $141.42   10.757%   $156.6325   $156.63   $156.65   $156.60  
  Purchase #3 $58.73   8.811%   $63.9047   $63.90   $63.90   $63.90  
  Purchase #4 $15.41   8.419%   $16.7074   $16.71   $16.70   $16.70  
  Purchase #5 $202.34   12.862%   $228.365   $228.37   $228.35   $228.40  
  Purchase #6 $101.76   11.418%   $113.379   $113.38   $113.40   $113.40  
  Purchase #7 $111.59   13.354%   $126.4917   $126.49   $126.50   $126.50  
  7 purchase totals = $713.04       $798.4085   $798.41   $798.45   $798.40