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 $183.83   6.612%   $195.9848   $195.98   $196.00   $196.00  
  Purchase #2 $140.95   8.228%   $152.5474   $152.55   $152.55   $152.50  
  Purchase #3 $212.25   11.136%   $235.8862   $235.89   $235.90   $235.90  
  Purchase #4 $37.75   11.225%   $41.9874   $41.99   $42.00   $42.00  
  Purchase #5 $59.94   10.241%   $66.0785   $66.08   $66.10   $66.10  
  Purchase #6 $52.55   6.557%   $55.9957   $56.00   $56.00   $56.00  
  Purchase #7 $237.35   5.174%   $249.6305   $249.63   $249.65   $249.60  
  7 purchase totals = $924.62       $998.1105   $998.12   $998.20   $998.10