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 $44.61   4.136%   $46.4551   $46.46   $46.45   $46.50  
  Purchase #2 $109.85   11.255%   $122.2136   $122.21   $122.20   $122.20  
  Purchase #3 $230.78   3.841%   $239.6443   $239.64   $239.65   $239.60  
  Purchase #4 $114.72   3.797%   $119.0759   $119.08   $119.10   $119.10  
  Purchase #5 $222.46   6.372%   $236.6352   $236.64   $236.65   $236.60  
  Purchase #6 $72.94   7.739%   $78.5848   $78.58   $78.60   $78.60  
  Purchase #7 $232.94   12.342%   $261.6895   $261.69   $261.70   $261.70  
  7 purchase totals = $1,028.30       $1,104.2984   $1,104.30   $1,104.35   $1,104.30