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 $208.67   13.262%   $236.3438   $236.34   $236.35   $236.30  
  Purchase #2 $242.38   4.278%   $252.749   $252.75   $252.75   $252.70  
  Purchase #3 $178.91   3.828%   $185.7587   $185.76   $185.75   $185.80  
  Purchase #4 $212.32   9.772%   $233.0679   $233.07   $233.05   $233.10  
  Purchase #5 $9.27   5.374%   $9.7682   $9.77   $9.75   $9.80  
  Purchase #6 $24.38   9.723%   $26.7505   $26.75   $26.75   $26.80  
  Purchase #7 $122.90   6.747%   $131.1921   $131.19   $131.20   $131.20  
  7 purchase totals = $998.83       $1,075.6302   $1,075.63   $1,075.60   $1,075.70