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 $23.62   13.144%   $26.7246   $26.72   $26.70   $26.70  
  Purchase #2 $29.28   4.469%   $30.5885   $30.59   $30.60   $30.60  
  Purchase #3 $40.81   3.827%   $42.3718   $42.37   $42.35   $42.40  
  Purchase #4 $6.71   7.382%   $7.2053   $7.21   $7.20   $7.20  
  Purchase #5 $82.27   7.615%   $88.5349   $88.53   $88.55   $88.50  
  Purchase #6 $6.66   13.509%   $7.5597   $7.56   $7.55   $7.60  
  Purchase #7 $139.34   12.786%   $157.156   $157.16   $157.15   $157.20  
  7 purchase totals = $328.69       $360.1408   $360.14   $360.10   $360.20