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 $216.71   11.552%   $241.7443   $241.74   $241.75   $241.70  
  Purchase #2 $68.75   13.398%   $77.9611   $77.96   $77.95   $78.00  
  Purchase #3 $24.46   6.462%   $26.0406   $26.04   $26.05   $26.00  
  Purchase #4 $166.80   4.253%   $173.894   $173.89   $173.90   $173.90  
  Purchase #5 $50.80   9.739%   $55.7474   $55.75   $55.75   $55.70  
  Purchase #6 $239.76   9.243%   $261.921   $261.92   $261.90   $261.90  
  Purchase #7 $196.32   9.241%   $214.4619   $214.46   $214.45   $214.50  
  7 purchase totals = $963.60       $1,051.7703   $1,051.76   $1,051.75   $1,051.70