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 $222.38   6.783%   $237.464   $237.46   $237.45   $237.50  
  Purchase #2 $31.37   3.282%   $32.3996   $32.40   $32.40   $32.40  
  Purchase #3 $125.46   8.293%   $135.8644   $135.86   $135.85   $135.90  
  Purchase #4 $59.93   4.721%   $62.7593   $62.76   $62.75   $62.80  
  Purchase #5 $78.71   3.739%   $81.653   $81.65   $81.65   $81.70  
  Purchase #6 $233.46   12.194%   $261.9281   $261.93   $261.95   $261.90  
  Purchase #7 $225.36   11.135%   $250.4538   $250.45   $250.45   $250.50  
  7 purchase totals = $976.67       $1,062.5222   $1,062.51   $1,062.50   $1,062.70