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 $72.41   13.570%   $82.236   $82.24   $82.25   $82.20  
  Purchase #2 $41.46   7.349%   $44.5069   $44.51   $44.50   $44.50  
  Purchase #3 $164.26   6.567%   $175.047   $175.05   $175.05   $175.00  
  Purchase #4 $190.25   4.311%   $198.4517   $198.45   $198.45   $198.50  
  Purchase #5 $35.95   5.141%   $37.7982   $37.80   $37.80   $37.80  
  Purchase #6 $232.76   6.789%   $248.5621   $248.56   $248.55   $248.60  
  Purchase #7 $182.37   13.171%   $206.39   $206.39   $206.40   $206.40  
  7 purchase totals = $919.46       $992.9919   $993.00   $993.00   $993.00