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 $239.87   6.811%   $256.2075   $256.21   $256.20   $256.20  
  Purchase #2 $227.48   10.537%   $251.4496   $251.45   $251.45   $251.40  
  Purchase #3 $64.99   3.751%   $67.4278   $67.43   $67.45   $67.40  
  Purchase #4 $210.78   5.492%   $222.356   $222.36   $222.35   $222.40  
  Purchase #5 $184.94   3.238%   $190.9284   $190.93   $190.95   $190.90  
  Purchase #6 $112.81   3.137%   $116.3488   $116.35   $116.35   $116.30  
  Purchase #7 $60.55   6.296%   $64.3622   $64.36   $64.35   $64.40  
  7 purchase totals = $1,101.42       $1,169.0803   $1,169.09   $1,169.10   $1,169.00