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 $229.63   13.747%   $261.1972   $261.20   $261.20   $261.20  
  Purchase #2 $8.35   5.546%   $8.8131   $8.81   $8.80   $8.80  
  Purchase #3 $156.90   7.545%   $168.7381   $168.74   $168.75   $168.70  
  Purchase #4 $236.61   5.779%   $250.2837   $250.28   $250.30   $250.30  
  Purchase #5 $202.86   10.804%   $224.777   $224.78   $224.80   $224.80  
  Purchase #6 $222.34   5.739%   $235.1001   $235.10   $235.10   $235.10  
  Purchase #7 $61.45   3.272%   $63.4606   $63.46   $63.45   $63.50  
  7 purchase totals = $1,118.14       $1,212.3698   $1,212.37   $1,212.40   $1,212.40