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 $217.82   13.183%   $246.5352   $246.54   $246.55   $246.50  
  Purchase #2 $230.66   8.752%   $250.8474   $250.85   $250.85   $250.80  
  Purchase #3 $83.38   5.385%   $87.87   $87.87   $87.85   $87.90  
  Purchase #4 $137.71   4.300%   $143.6315   $143.63   $143.65   $143.60  
  Purchase #5 $234.25   9.638%   $256.827   $256.83   $256.85   $256.80  
  Purchase #6 $41.80   9.788%   $45.8914   $45.89   $45.90   $45.90  
  Purchase #7 $173.88   12.366%   $195.382   $195.38   $195.40   $195.40  
  7 purchase totals = $1,119.50       $1,226.9845   $1,226.99   $1,227.05   $1,226.90