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 $217.69   8.240%   $235.6277   $235.63   $235.65   $235.60  
  Purchase #2 $40.33   8.562%   $43.7831   $43.78   $43.80   $43.80  
  Purchase #3 $120.75   11.494%   $134.629   $134.63   $134.65   $134.60  
  Purchase #4 $46.84   4.739%   $49.0597   $49.06   $49.05   $49.10  
  Purchase #5 $78.81   5.400%   $83.0657   $83.07   $83.05   $83.10  
  Purchase #6 $74.44   10.511%   $82.2644   $82.26   $82.25   $82.30  
  Purchase #7 $190.95   8.177%   $206.564   $206.56   $206.55   $206.60  
  7 purchase totals = $769.81       $834.9936   $834.99   $835.00   $835.10