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 $188.53   10.322%   $207.9901   $207.99   $208.00   $208.00  
  Purchase #2 $48.66   4.332%   $50.768   $50.77   $50.75   $50.80  
  Purchase #3 $138.95   8.301%   $150.4842   $150.48   $150.50   $150.50  
  Purchase #4 $136.85   13.182%   $154.8896   $154.89   $154.90   $154.90  
  Purchase #5 $66.54   13.593%   $75.5848   $75.58   $75.60   $75.60  
  Purchase #6 $52.25   7.755%   $56.302   $56.30   $56.30   $56.30  
  Purchase #7 $177.29   5.197%   $186.5038   $186.50   $186.50   $186.50  
  7 purchase totals = $809.07       $882.5225   $882.51   $882.55   $882.60