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 $250.36   4.453%   $261.5085   $261.51   $261.50   $261.50  
  Purchase #2 $150.25   8.669%   $163.2752   $163.28   $163.30   $163.30  
  Purchase #3 $55.70   8.713%   $60.5531   $60.55   $60.55   $60.60  
  Purchase #4 $203.30   5.617%   $214.7194   $214.72   $214.70   $214.70  
  Purchase #5 $200.31   9.641%   $219.6219   $219.62   $219.60   $219.60  
  Purchase #6 $135.69   4.207%   $141.3985   $141.40   $141.40   $141.40  
  Purchase #7 $49.86   6.428%   $53.065   $53.07   $53.05   $53.10  
  7 purchase totals = $1,045.47       $1,114.1416   $1,114.15   $1,114.10   $1,114.20