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 $214.56   11.641%   $239.5369   $239.54   $239.55   $239.50  
  Purchase #2 $250.63   12.394%   $281.6931   $281.69   $281.70   $281.70  
  Purchase #3 $132.32   7.151%   $141.7822   $141.78   $141.80   $141.80  
  Purchase #4 $110.27   11.607%   $123.069   $123.07   $123.05   $123.10  
  Purchase #5 $13.26   12.514%   $14.9194   $14.92   $14.90   $14.90  
  Purchase #6 $224.95   5.136%   $236.5034   $236.50   $236.50   $236.50  
  Purchase #7 $192.98   7.426%   $207.3107   $207.31   $207.30   $207.30  
  7 purchase totals = $1,138.97       $1,244.8147   $1,244.81   $1,244.80   $1,244.80