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 $214.36   11.745%   $239.5366   $239.54   $239.55   $239.50  
  Purchase #2 $217.25   9.448%   $237.7758   $237.78   $237.80   $237.80  
  Purchase #3 $129.85   7.801%   $139.9796   $139.98   $140.00   $140.00  
  Purchase #4 $139.53   9.334%   $152.5537   $152.55   $152.55   $152.60  
  Purchase #5 $163.72   11.661%   $182.8114   $182.81   $182.80   $182.80  
  Purchase #6 $185.35   4.242%   $193.2125   $193.21   $193.20   $193.20  
  Purchase #7 $95.91   8.555%   $104.1151   $104.12   $104.10   $104.10  
  7 purchase totals = $1,145.97       $1,249.9847   $1,249.99   $1,250.00   $1,250.00