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 $173.90   13.229%   $196.9052   $196.91   $196.90   $196.90  
  Purchase #2 $248.63   12.314%   $279.2463   $279.25   $279.25   $279.20  
  Purchase #3 $178.35   13.678%   $202.7447   $202.74   $202.75   $202.70  
  Purchase #4 $70.66   5.266%   $74.381   $74.38   $74.40   $74.40  
  Purchase #5 $236.46   9.262%   $258.3609   $258.36   $258.35   $258.40  
  Purchase #6 $8.73   6.805%   $9.3241   $9.32   $9.30   $9.30  
  Purchase #7 $179.98   8.418%   $195.1307   $195.13   $195.15   $195.10  
  7 purchase totals = $1,096.71       $1,216.0929   $1,216.09   $1,216.10   $1,216.00