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 $86.51   8.151%   $93.5614   $93.56   $93.55   $93.60  
  Purchase #2 $114.67   11.119%   $127.4202   $127.42   $127.40   $127.40  
  Purchase #3 $122.87   13.454%   $139.4009   $139.40   $139.40   $139.40  
  Purchase #4 $73.32   12.452%   $82.4498   $82.45   $82.45   $82.40  
  Purchase #5 $30.27   12.829%   $34.1533   $34.15   $34.15   $34.20  
  Purchase #6 $190.54   6.187%   $202.3287   $202.33   $202.35   $202.30  
  Purchase #7 $250.57   10.307%   $276.3962   $276.40   $276.40   $276.40  
  7 purchase totals = $868.75       $955.7105   $955.71   $955.70   $955.70