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 $235.87   5.795%   $249.5387   $249.54   $249.55   $249.50  
  Purchase #2 $213.68   10.647%   $236.4305   $236.43   $236.45   $236.40  
  Purchase #3 $224.63   9.874%   $246.81   $246.81   $246.80   $246.80  
  Purchase #4 $146.92   11.266%   $163.472   $163.47   $163.45   $163.50  
  Purchase #5 $45.69   3.471%   $47.2759   $47.28   $47.30   $47.30  
  Purchase #6 $97.60   10.284%   $107.6372   $107.64   $107.65   $107.60  
  Purchase #7 $45.64   4.423%   $47.6587   $47.66   $47.65   $47.70  
  7 purchase totals = $1,010.03       $1,098.8230   $1,098.83   $1,098.85   $1,098.80