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 $118.96   10.174%   $131.063   $131.06   $131.05   $131.10  
  Purchase #2 $175.41   7.246%   $188.1202   $188.12   $188.10   $188.10  
  Purchase #3 $179.83   12.710%   $202.6864   $202.69   $202.70   $202.70  
  Purchase #4 $236.26   10.760%   $261.6816   $261.68   $261.70   $261.70  
  Purchase #5 $84.79   11.723%   $94.7299   $94.73   $94.75   $94.70  
  Purchase #6 $185.28   4.436%   $193.499   $193.50   $193.50   $193.50  
  Purchase #7 $210.43   7.871%   $226.9929   $226.99   $227.00   $227.00  
  7 purchase totals = $1,190.96       $1,298.7730   $1,298.77   $1,298.80   $1,298.80