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 $78.32   6.659%   $83.5353   $83.54   $83.55   $83.50  
  Purchase #2 $248.79   8.326%   $269.5043   $269.50   $269.50   $269.50  
  Purchase #3 $132.69   3.156%   $136.8777   $136.88   $136.90   $136.90  
  Purchase #4 $69.36   5.486%   $73.1651   $73.17   $73.15   $73.20  
  Purchase #5 $63.67   9.346%   $69.6206   $69.62   $69.60   $69.60  
  Purchase #6 $207.29   13.197%   $234.6461   $234.65   $234.65   $234.60  
  Purchase #7 $137.89   3.308%   $142.4514   $142.45   $142.45   $142.50  
  7 purchase totals = $938.01       $1,009.8005   $1,009.81   $1,009.80   $1,009.80