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 $34.82   11.121%   $38.6923   $38.69   $38.70   $38.70  
  Purchase #2 $49.91   12.392%   $56.0948   $56.09   $56.10   $56.10  
  Purchase #3 $218.79   9.604%   $239.8026   $239.80   $239.80   $239.80  
  Purchase #4 $219.88   9.277%   $240.2783   $240.28   $240.30   $240.30  
  Purchase #5 $107.53   6.383%   $114.3936   $114.39   $114.40   $114.40  
  Purchase #6 $210.89   10.863%   $233.799   $233.80   $233.80   $233.80  
  Purchase #7 $76.51   12.304%   $85.9238   $85.92   $85.90   $85.90  
  7 purchase totals = $918.33       $1,008.9844   $1,008.97   $1,009.00   $1,009.00