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 $164.77   12.583%   $185.503   $185.50   $185.50   $185.50  
  Purchase #2 $249.42   4.217%   $259.938   $259.94   $259.95   $259.90  
  Purchase #3 $151.38   9.765%   $166.1623   $166.16   $166.15   $166.20  
  Purchase #4 $93.57   5.407%   $98.6293   $98.63   $98.65   $98.60  
  Purchase #5 $24.43   4.285%   $25.4768   $25.48   $25.50   $25.50  
  Purchase #6 $243.81   9.822%   $267.757   $267.76   $267.75   $267.80  
  Purchase #7 $218.25   11.544%   $243.4448   $243.44   $243.45   $243.40  
  7 purchase totals = $1,145.63       $1,246.9112   $1,246.91   $1,246.95   $1,246.90