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 $118.45   13.683%   $134.6575   $134.66   $134.65   $134.70  
  Purchase #2 $25.78   3.162%   $26.5952   $26.60   $26.60   $26.60  
  Purchase #3 $88.35   10.789%   $97.8821   $97.88   $97.90   $97.90  
  Purchase #4 $230.41   4.755%   $241.366   $241.37   $241.35   $241.40  
  Purchase #5 $182.32   3.558%   $188.8069   $188.81   $188.80   $188.80  
  Purchase #6 $7.58   8.724%   $8.2413   $8.24   $8.25   $8.20  
  Purchase #7 $238.93   9.364%   $261.3034   $261.30   $261.30   $261.30  
  7 purchase totals = $891.82       $958.8524   $958.86   $958.85   $958.90