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 $247.85   5.523%   $261.5388   $261.54   $261.55   $261.50  
  Purchase #2 $131.82   6.583%   $140.4977   $140.50   $140.50   $140.50  
  Purchase #3 $225.50   10.617%   $249.4413   $249.44   $249.45   $249.40  
  Purchase #4 $25.85   10.623%   $28.596   $28.60   $28.60   $28.60  
  Purchase #5 $87.49   8.142%   $94.6134   $94.61   $94.60   $94.60  
  Purchase #6 $176.35   5.708%   $186.4161   $186.42   $186.40   $186.40  
  Purchase #7 $24.28   8.489%   $26.3411   $26.34   $26.35   $26.30  
  7 purchase totals = $919.14       $987.4444   $987.45   $987.45   $987.30