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 $207.86   3.562%   $215.264   $215.26   $215.25   $215.30  
  Purchase #2 $74.98   8.786%   $81.5677   $81.57   $81.55   $81.60  
  Purchase #3 $41.81   6.734%   $44.6255   $44.63   $44.65   $44.60  
  Purchase #4 $201.28   8.271%   $217.9279   $217.93   $217.95   $217.90  
  Purchase #5 $114.75   4.664%   $120.1019   $120.10   $120.10   $120.10  
  Purchase #6 $58.72   10.117%   $64.6607   $64.66   $64.65   $64.70  
  Purchase #7 $100.27   12.414%   $112.7175   $112.72   $112.70   $112.70  
  7 purchase totals = $799.67       $856.8652   $856.87   $856.85   $856.90