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 $227.81   13.473%   $258.5028   $258.50   $258.50   $258.50  
  Purchase #2 $171.94   8.446%   $186.4621   $186.46   $186.45   $186.50  
  Purchase #3 $43.61   11.478%   $48.6156   $48.62   $48.60   $48.60  
  Purchase #4 $233.77   8.377%   $253.3529   $253.35   $253.35   $253.40  
  Purchase #5 $174.56   10.319%   $192.5728   $192.57   $192.55   $192.60  
  Purchase #6 $239.40   3.451%   $247.6617   $247.66   $247.65   $247.70  
  Purchase #7 $70.86   4.225%   $73.8538   $73.85   $73.85   $73.90  
  7 purchase totals = $1,161.95       $1,261.0217   $1,261.01   $1,260.95   $1,261.20