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 $33.77   8.292%   $36.5702   $36.57   $36.55   $36.60  
  Purchase #2 $248.62   13.544%   $282.2931   $282.29   $282.30   $282.30  
  Purchase #3 $238.48   5.202%   $250.8857   $250.89   $250.90   $250.90  
  Purchase #4 $63.82   11.741%   $71.3131   $71.31   $71.30   $71.30  
  Purchase #5 $191.99   12.108%   $215.2361   $215.24   $215.25   $215.20  
  Purchase #6 $114.98   9.318%   $125.6938   $125.69   $125.70   $125.70  
  Purchase #7 $77.78   9.826%   $85.4227   $85.42   $85.40   $85.40  
  7 purchase totals = $969.44       $1,067.4147   $1,067.41   $1,067.40   $1,067.40