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 $23.92   11.752%   $26.7311   $26.73   $26.75   $26.70  
  Purchase #2 $107.54   6.242%   $114.2526   $114.25   $114.25   $114.30  
  Purchase #3 $210.42   5.697%   $222.4076   $222.41   $222.40   $222.40  
  Purchase #4 $179.61   8.308%   $194.532   $194.53   $194.55   $194.50  
  Purchase #5 $29.89   4.636%   $31.2757   $31.28   $31.30   $31.30  
  Purchase #6 $225.95   11.473%   $251.8732   $251.87   $251.85   $251.90  
  Purchase #7 $172.48   13.149%   $195.1594   $195.16   $195.15   $195.20  
  7 purchase totals = $949.81       $1,036.2316   $1,036.23   $1,036.25   $1,036.30