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 $114.28   3.756%   $118.5724   $118.57   $118.55   $118.60  
  Purchase #2 $65.31   4.522%   $68.2633   $68.26   $68.25   $68.30  
  Purchase #3 $196.55   6.632%   $209.5852   $209.59   $209.60   $209.60  
  Purchase #4 $53.81   4.291%   $56.119   $56.12   $56.10   $56.10  
  Purchase #5 $57.77   13.864%   $65.7792   $65.78   $65.80   $65.80  
  Purchase #6 $242.83   13.376%   $275.3109   $275.31   $275.30   $275.30  
  Purchase #7 $24.73   5.451%   $26.078   $26.08   $26.10   $26.10  
  7 purchase totals = $755.28       $819.7080   $819.71   $819.70   $819.80