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 $152.95   5.862%   $161.9159   $161.92   $161.90   $161.90  
  Purchase #2 $22.81   8.675%   $24.7888   $24.79   $24.80   $24.80  
  Purchase #3 $51.29   3.718%   $53.197   $53.20   $53.20   $53.20  
  Purchase #4 $210.25   4.757%   $220.2516   $220.25   $220.25   $220.30  
  Purchase #5 $53.81   3.211%   $55.5378   $55.54   $55.55   $55.50  
  Purchase #6 $27.69   9.306%   $30.2668   $30.27   $30.25   $30.30  
  Purchase #7 $176.55   7.729%   $190.1955   $190.20   $190.20   $190.20  
  7 purchase totals = $695.35       $736.1534   $736.17   $736.15   $736.20