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 $56.64   12.662%   $63.8118   $63.81   $63.80   $63.80  
  Purchase #2 $23.45   4.274%   $24.4523   $24.45   $24.45   $24.50  
  Purchase #3 $177.68   9.122%   $193.888   $193.89   $193.90   $193.90  
  Purchase #4 $240.26   3.841%   $249.4884   $249.49   $249.50   $249.50  
  Purchase #5 $56.69   3.377%   $58.6044   $58.60   $58.60   $58.60  
  Purchase #6 $165.85   6.855%   $177.219   $177.22   $177.20   $177.20  
  Purchase #7 $90.59   13.255%   $102.5977   $102.60   $102.60   $102.60  
  7 purchase totals = $811.16       $870.0616   $870.06   $870.05   $870.10