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 $171.73   11.756%   $191.9186   $191.92   $191.90   $191.90  
  Purchase #2 $248.25   5.151%   $261.0374   $261.04   $261.05   $261.00  
  Purchase #3 $238.92   4.761%   $250.295   $250.30   $250.30   $250.30  
  Purchase #4 $117.55   5.550%   $124.074   $124.07   $124.05   $124.10  
  Purchase #5 $95.87   9.466%   $104.9451   $104.95   $104.95   $104.90  
  Purchase #6 $187.99   6.670%   $200.5289   $200.53   $200.55   $200.50  
  Purchase #7 $117.96   5.459%   $124.3994   $124.40   $124.40   $124.40  
  7 purchase totals = $1,178.27       $1,257.1984   $1,257.21   $1,257.20   $1,257.10