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 $203.50   13.816%   $231.6156   $231.62   $231.60   $231.60  
  Purchase #2 $177.76   11.230%   $197.7224   $197.72   $197.70   $197.70  
  Purchase #3 $186.89   3.694%   $193.7937   $193.79   $193.80   $193.80  
  Purchase #4 $59.33   8.273%   $64.2384   $64.24   $64.25   $64.20  
  Purchase #5 $242.37   7.867%   $261.4372   $261.44   $261.45   $261.40  
  Purchase #6 $40.32   12.735%   $45.4548   $45.45   $45.45   $45.50  
  Purchase #7 $45.74   7.715%   $49.2688   $49.27   $49.25   $49.30  
  7 purchase totals = $955.91       $1,043.5309   $1,043.53   $1,043.50   $1,043.50