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 $57.32   12.107%   $64.2597   $64.26   $64.25   $64.30  
  Purchase #2 $153.63   4.356%   $160.3221   $160.32   $160.30   $160.30  
  Purchase #3 $130.42   4.810%   $136.6932   $136.69   $136.70   $136.70  
  Purchase #4 $74.85   4.641%   $78.3238   $78.32   $78.30   $78.30  
  Purchase #5 $95.76   13.718%   $108.8964   $108.90   $108.90   $108.90  
  Purchase #6 $240.45   9.681%   $263.728   $263.73   $263.75   $263.70  
  Purchase #7 $41.78   6.791%   $44.6173   $44.62   $44.60   $44.60  
  7 purchase totals = $794.21       $856.8405   $856.84   $856.80   $856.80