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 $239.28   11.479%   $266.747   $266.75   $266.75   $266.70  
  Purchase #2 $109.78   13.284%   $124.3632   $124.36   $124.35   $124.40  
  Purchase #3 $186.46   3.656%   $193.277   $193.28   $193.30   $193.30  
  Purchase #4 $226.67   10.721%   $250.9713   $250.97   $250.95   $251.00  
  Purchase #5 $146.61   13.544%   $166.4669   $166.47   $166.45   $166.50  
  Purchase #6 $217.71   13.241%   $246.537   $246.54   $246.55   $246.50  
  Purchase #7 $97.81   9.697%   $107.2946   $107.29   $107.30   $107.30  
  7 purchase totals = $1,224.32       $1,355.6570   $1,355.66   $1,355.65   $1,355.70