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 $24.71   5.858%   $26.1575   $26.16   $26.15   $26.20  
  Purchase #2 $57.35   12.794%   $64.6874   $64.69   $64.70   $64.70  
  Purchase #3 $246.34   10.181%   $271.4199   $271.42   $271.40   $271.40  
  Purchase #4 $54.54   3.722%   $56.57   $56.57   $56.55   $56.60  
  Purchase #5 $207.67   8.410%   $225.135   $225.14   $225.15   $225.10  
  Purchase #6 $225.54   6.772%   $240.8136   $240.81   $240.80   $240.80  
  Purchase #7 $78.43   4.665%   $82.0888   $82.09   $82.10   $82.10  
  7 purchase totals = $894.58       $966.8722   $966.88   $966.85   $966.90