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 $104.93   13.272%   $118.8563   $118.86   $118.85   $118.90  
  Purchase #2 $227.39   4.226%   $236.9995   $237.00   $237.00   $237.00  
  Purchase #3 $15.73   4.276%   $16.4026   $16.40   $16.40   $16.40  
  Purchase #4 $161.76   5.110%   $170.0259   $170.03   $170.05   $170.00  
  Purchase #5 $107.70   6.728%   $114.9461   $114.95   $114.95   $114.90  
  Purchase #6 $149.46   4.757%   $156.5698   $156.57   $156.55   $156.60  
  Purchase #7 $239.86   9.250%   $262.0471   $262.05   $262.05   $262.00  
  7 purchase totals = $1,006.83       $1,075.8473   $1,075.86   $1,075.85   $1,075.80