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 $207.39   13.592%   $235.5784   $235.58   $235.60   $235.60  
  Purchase #2 $238.45   4.719%   $249.7025   $249.70   $249.70   $249.70  
  Purchase #3 $96.26   6.237%   $102.2637   $102.26   $102.25   $102.30  
  Purchase #4 $128.44   8.485%   $139.3381   $139.34   $139.35   $139.30  
  Purchase #5 $186.69   11.285%   $207.758   $207.76   $207.75   $207.80  
  Purchase #6 $32.70   4.358%   $34.1251   $34.13   $34.15   $34.10  
  Purchase #7 $107.91   6.377%   $114.7914   $114.79   $114.80   $114.80  
  7 purchase totals = $997.84       $1,083.5572   $1,083.56   $1,083.60   $1,083.60