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 $111.26   13.864%   $126.6851   $126.69   $126.70   $126.70  
  Purchase #2 $239.70   9.593%   $262.6944   $262.69   $262.70   $262.70  
  Purchase #3 $156.37   5.872%   $165.552   $165.55   $165.55   $165.60  
  Purchase #4 $130.71   7.723%   $140.8047   $140.80   $140.80   $140.80  
  Purchase #5 $39.70   10.212%   $43.7542   $43.75   $43.75   $43.80  
  Purchase #6 $37.41   3.177%   $38.5985   $38.60   $38.60   $38.60  
  Purchase #7 $12.37   3.437%   $12.7952   $12.80   $12.80   $12.80  
  7 purchase totals = $727.52       $790.8841   $790.88   $790.90   $791.00