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 $219.55   3.664%   $227.5943   $227.59   $227.60   $227.60  
  Purchase #2 $223.48   4.600%   $233.7601   $233.76   $233.75   $233.80  
  Purchase #3 $137.32   12.137%   $153.9865   $153.99   $154.00   $154.00  
  Purchase #4 $213.42   6.389%   $227.0554   $227.06   $227.05   $227.10  
  Purchase #5 $143.64   10.626%   $158.9032   $158.90   $158.90   $158.90  
  Purchase #6 $242.45   9.586%   $265.6913   $265.69   $265.70   $265.70  
  Purchase #7 $64.31   10.409%   $71.004   $71.00   $71.00   $71.00  
  7 purchase totals = $1,244.17       $1,337.9948   $1,337.99   $1,338.00   $1,338.10