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 $185.26   12.783%   $208.9418   $208.94   $208.95   $208.90  
  Purchase #2 $60.32   4.188%   $62.8462   $62.85   $62.85   $62.80  
  Purchase #3 $54.29   12.783%   $61.2299   $61.23   $61.25   $61.20  
  Purchase #4 $164.40   3.351%   $169.909   $169.91   $169.90   $169.90  
  Purchase #5 $233.59   6.839%   $249.5652   $249.57   $249.55   $249.60  
  Purchase #6 $196.29   5.554%   $207.1919   $207.19   $207.20   $207.20  
  Purchase #7 $215.91   3.685%   $223.8663   $223.87   $223.85   $223.90  
  7 purchase totals = $1,110.06       $1,183.5503   $1,183.56   $1,183.55   $1,183.50