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 $78.41   5.323%   $82.5838   $82.58   $82.60   $82.60  
  Purchase #2 $112.42   5.538%   $118.6458   $118.65   $118.65   $118.60  
  Purchase #3 $200.90   4.440%   $209.82   $209.82   $209.80   $209.80  
  Purchase #4 $141.67   13.416%   $160.6764   $160.68   $160.70   $160.70  
  Purchase #5 $114.33   6.783%   $122.085   $122.09   $122.10   $122.10  
  Purchase #6 $190.58   5.595%   $201.243   $201.24   $201.25   $201.20  
  Purchase #7 $58.27   4.499%   $60.8916   $60.89   $60.90   $60.90  
  7 purchase totals = $896.58       $955.9456   $955.95   $956.00   $955.90