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 $236.71   6.670%   $252.4986   $252.50   $252.50   $252.50  
  Purchase #2 $174.71   5.143%   $183.6953   $183.70   $183.70   $183.70  
  Purchase #3 $116.47   8.697%   $126.5994   $126.60   $126.60   $126.60  
  Purchase #4 $151.63   12.514%   $170.605   $170.61   $170.60   $170.60  
  Purchase #5 $83.44   3.231%   $86.1359   $86.14   $86.15   $86.10  
  Purchase #6 $82.63   6.575%   $88.0629   $88.06   $88.05   $88.10  
  Purchase #7 $150.48   11.844%   $168.3029   $168.30   $168.30   $168.30  
  7 purchase totals = $996.07       $1,075.9000   $1,075.91   $1,075.90   $1,075.90