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 $60.34   9.730%   $66.2111   $66.21   $66.20   $66.20  
  Purchase #2 $141.47   11.843%   $158.2243   $158.22   $158.20   $158.20  
  Purchase #3 $52.49   7.271%   $56.3065   $56.31   $56.30   $56.30  
  Purchase #4 $63.41   7.252%   $68.0085   $68.01   $68.00   $68.00  
  Purchase #5 $192.97   7.263%   $206.9854   $206.99   $207.00   $207.00  
  Purchase #6 $174.76   12.270%   $196.2031   $196.20   $196.20   $196.20  
  Purchase #7 $9.92   8.105%   $10.724   $10.72   $10.70   $10.70  
  7 purchase totals = $695.36       $762.6629   $762.66   $762.60   $762.60