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 $142.79   9.634%   $156.5464   $156.55   $156.55   $156.50  
  Purchase #2 $203.35   11.106%   $225.9341   $225.93   $225.95   $225.90  
  Purchase #3 $119.36   6.130%   $126.6768   $126.68   $126.70   $126.70  
  Purchase #4 $23.74   12.768%   $26.7711   $26.77   $26.75   $26.80  
  Purchase #5 $168.86   12.605%   $190.1448   $190.14   $190.15   $190.10  
  Purchase #6 $14.51   4.408%   $15.1496   $15.15   $15.15   $15.10  
  Purchase #7 $48.71   9.725%   $53.447   $53.45   $53.45   $53.40  
  7 purchase totals = $721.32       $794.6698   $794.67   $794.70   $794.50