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 $205.69   10.707%   $227.7132   $227.71   $227.70   $227.70  
  Purchase #2 $67.28   10.848%   $74.5785   $74.58   $74.60   $74.60  
  Purchase #3 $108.34   4.684%   $113.4146   $113.41   $113.40   $113.40  
  Purchase #4 $186.54   8.638%   $202.6533   $202.65   $202.65   $202.70  
  Purchase #5 $152.83   4.296%   $159.3956   $159.40   $159.40   $159.40  
  Purchase #6 $134.28   13.189%   $151.9902   $151.99   $152.00   $152.00  
  Purchase #7 $72.87   5.122%   $76.6024   $76.60   $76.60   $76.60  
  7 purchase totals = $927.83       $1,006.3478   $1,006.34   $1,006.35   $1,006.40