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 $248.89   5.336%   $262.1708   $262.17   $262.15   $262.20  
  Purchase #2 $232.86   11.660%   $260.0115   $260.01   $260.00   $260.00  
  Purchase #3 $114.82   5.755%   $121.4279   $121.43   $121.45   $121.40  
  Purchase #4 $60.35   4.554%   $63.0983   $63.10   $63.10   $63.10  
  Purchase #5 $226.25   9.493%   $247.7279   $247.73   $247.75   $247.70  
  Purchase #6 $133.65   7.292%   $143.3958   $143.40   $143.40   $143.40  
  Purchase #7 $121.46   10.768%   $134.5388   $134.54   $134.55   $134.50  
  7 purchase totals = $1,138.28       $1,232.3710   $1,232.38   $1,232.40   $1,232.30