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 $208.94   13.103%   $236.3174   $236.32   $236.30   $236.30  
  Purchase #2 $123.71   10.379%   $136.5499   $136.55   $136.55   $136.50  
  Purchase #3 $110.30   11.724%   $123.2316   $123.23   $123.25   $123.20  
  Purchase #4 $247.68   7.393%   $265.991   $265.99   $266.00   $266.00  
  Purchase #5 $185.27   8.448%   $200.9216   $200.92   $200.90   $200.90  
  Purchase #6 $202.34   4.313%   $211.0669   $211.07   $211.05   $211.10  
  Purchase #7 $24.58   7.410%   $26.4014   $26.40   $26.40   $26.40  
  7 purchase totals = $1,102.82       $1,200.4798   $1,200.48   $1,200.45   $1,200.40