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 $38.68   10.540%   $42.7569   $42.76   $42.75   $42.80  
  Purchase #2 $245.87   6.407%   $261.6229   $261.62   $261.60   $261.60  
  Purchase #3 $220.74   5.865%   $233.6864   $233.69   $233.70   $233.70  
  Purchase #4 $35.58   5.458%   $37.522   $37.52   $37.50   $37.50  
  Purchase #5 $198.46   7.421%   $213.1877   $213.19   $213.20   $213.20  
  Purchase #6 $237.34   10.600%   $262.498   $262.50   $262.50   $262.50  
  Purchase #7 $182.26   4.403%   $190.2849   $190.28   $190.30   $190.30  
  7 purchase totals = $1,158.93       $1,241.5588   $1,241.56   $1,241.55   $1,241.60