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 $232.87   12.294%   $261.499   $261.50   $261.50   $261.50  
  Purchase #2 $56.66   5.209%   $59.6114   $59.61   $59.60   $59.60  
  Purchase #3 $154.41   5.294%   $162.5845   $162.58   $162.60   $162.60  
  Purchase #4 $72.79   7.834%   $78.4924   $78.49   $78.50   $78.50  
  Purchase #5 $8.80   6.414%   $9.3644   $9.36   $9.35   $9.40  
  Purchase #6 $91.29   10.656%   $101.0179   $101.02   $101.00   $101.00  
  Purchase #7 $220.93   11.435%   $246.1933   $246.19   $246.20   $246.20  
  7 purchase totals = $837.75       $918.7629   $918.75   $918.75   $918.80