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 $207.92   6.804%   $222.0669   $222.07   $222.05   $222.10  
  Purchase #2 $132.39   4.714%   $138.6309   $138.63   $138.65   $138.60  
  Purchase #3 $248.73   11.187%   $276.5554   $276.56   $276.55   $276.60  
  Purchase #4 $208.57   13.569%   $236.8709   $236.87   $236.85   $236.90  
  Purchase #5 $235.74   7.161%   $252.6213   $252.62   $252.60   $252.60  
  Purchase #6 $198.53   6.209%   $210.8567   $210.86   $210.85   $210.90  
  Purchase #7 $75.83   4.379%   $79.1506   $79.15   $79.15   $79.20  
  7 purchase totals = $1,307.71       $1,416.7527   $1,416.76   $1,416.70   $1,416.90