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 $210.83   8.158%   $228.0295   $228.03   $228.05   $228.00  
  Purchase #2 $64.91   13.648%   $73.7689   $73.77   $73.75   $73.80  
  Purchase #3 $127.88   8.395%   $138.6155   $138.62   $138.60   $138.60  
  Purchase #4 $51.66   13.741%   $58.7586   $58.76   $58.75   $58.80  
  Purchase #5 $8.39   6.105%   $8.9022   $8.90   $8.90   $8.90  
  Purchase #6 $240.93   3.220%   $248.6879   $248.69   $248.70   $248.70  
  Purchase #7 $226.47   5.388%   $238.6722   $238.67   $238.65   $238.70  
  7 purchase totals = $931.07       $995.4348   $995.44   $995.40   $995.50