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 $60.68   7.868%   $65.4543   $65.45   $65.45   $65.50  
  Purchase #2 $114.78   3.757%   $119.0923   $119.09   $119.10   $119.10  
  Purchase #3 $232.93   7.596%   $250.6234   $250.62   $250.60   $250.60  
  Purchase #4 $48.78   9.329%   $53.3307   $53.33   $53.35   $53.30  
  Purchase #5 $114.71   5.376%   $120.8768   $120.88   $120.90   $120.90  
  Purchase #6 $207.34   12.723%   $233.7199   $233.72   $233.70   $233.70  
  Purchase #7 $118.33   13.386%   $134.1697   $134.17   $134.15   $134.20  
  7 purchase totals = $897.55       $977.2671   $977.26   $977.25   $977.30