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 $214.96   11.660%   $240.0243   $240.02   $240.00   $240.00  
  Purchase #2 $208.45   4.547%   $217.9282   $217.93   $217.95   $217.90  
  Purchase #3 $27.64   12.348%   $31.053   $31.05   $31.05   $31.10  
  Purchase #4 $236.69   4.445%   $247.2109   $247.21   $247.20   $247.20  
  Purchase #5 $77.56   12.719%   $87.4249   $87.42   $87.40   $87.40  
  Purchase #6 $146.61   13.330%   $166.1531   $166.15   $166.15   $166.20  
  Purchase #7 $168.60   11.105%   $187.323   $187.32   $187.30   $187.30  
  7 purchase totals = $1,080.51       $1,177.1174   $1,177.10   $1,177.05   $1,177.10