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 $50.95   9.581%   $55.8315   $55.83   $55.85   $55.80  
  Purchase #2 $167.57   4.863%   $175.7189   $175.72   $175.70   $175.70  
  Purchase #3 $50.88   3.585%   $52.704   $52.70   $52.70   $52.70  
  Purchase #4 $183.43   12.832%   $206.9677   $206.97   $206.95   $207.00  
  Purchase #5 $141.84   10.501%   $156.7346   $156.73   $156.75   $156.70  
  Purchase #6 $56.99   12.703%   $64.2294   $64.23   $64.25   $64.20  
  Purchase #7 $207.63   8.305%   $224.8737   $224.87   $224.85   $224.90  
  7 purchase totals = $859.29       $937.0598   $937.05   $937.05   $937.00