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 $119.70   3.545%   $123.9434   $123.94   $123.95   $123.90  
  Purchase #2 $161.71   9.313%   $176.7701   $176.77   $176.75   $176.80  
  Purchase #3 $27.63   4.126%   $28.77   $28.77   $28.75   $28.80  
  Purchase #4 $75.40   10.442%   $83.2733   $83.27   $83.25   $83.30  
  Purchase #5 $129.96   8.210%   $140.6297   $140.63   $140.65   $140.60  
  Purchase #6 $239.26   4.872%   $250.9167   $250.92   $250.90   $250.90  
  Purchase #7 $200.41   7.180%   $214.7994   $214.80   $214.80   $214.80  
  7 purchase totals = $954.07       $1,019.1026   $1,019.10   $1,019.05   $1,019.10