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 $235.32   13.726%   $267.62   $267.62   $267.60   $267.60  
  Purchase #2 $73.82   4.165%   $76.8946   $76.89   $76.90   $76.90  
  Purchase #3 $183.75   13.266%   $208.1263   $208.13   $208.15   $208.10  
  Purchase #4 $229.64   12.218%   $257.6974   $257.70   $257.70   $257.70  
  Purchase #5 $231.73   6.274%   $246.2687   $246.27   $246.25   $246.30  
  Purchase #6 $140.83   4.636%   $147.3589   $147.36   $147.35   $147.40  
  Purchase #7 $51.73   9.551%   $56.6707   $56.67   $56.65   $56.70  
  7 purchase totals = $1,146.82       $1,260.6366   $1,260.64   $1,260.60   $1,260.70