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 $208.67   13.428%   $236.6902   $236.69   $236.70   $236.70  
  Purchase #2 $141.77   7.401%   $152.2624   $152.26   $152.25   $152.30  
  Purchase #3 $246.81   4.861%   $258.8074   $258.81   $258.80   $258.80  
  Purchase #4 $24.31   13.262%   $27.534   $27.53   $27.55   $27.50  
  Purchase #5 $53.97   12.750%   $60.8512   $60.85   $60.85   $60.90  
  Purchase #6 $179.97   12.116%   $201.7752   $201.78   $201.80   $201.80  
  Purchase #7 $42.66   3.195%   $44.023   $44.02   $44.00   $44.00  
  7 purchase totals = $898.16       $981.9434   $981.94   $981.95   $982.00