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 $183.91   10.147%   $202.5713   $202.57   $202.55   $202.60  
  Purchase #2 $237.83   4.539%   $248.6251   $248.63   $248.65   $248.60  
  Purchase #3 $222.61   11.735%   $248.7333   $248.73   $248.75   $248.70  
  Purchase #4 $159.56   4.611%   $166.9173   $166.92   $166.90   $166.90  
  Purchase #5 $228.59   12.521%   $257.2118   $257.21   $257.20   $257.20  
  Purchase #6 $238.99   8.567%   $259.4643   $259.46   $259.45   $259.50  
  Purchase #7 $177.97   4.126%   $185.313   $185.31   $185.30   $185.30  
  7 purchase totals = $1,449.46       $1,568.8361   $1,568.83   $1,568.80   $1,568.80