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 $52.91   9.248%   $57.8031   $57.80   $57.80   $57.80  
  Purchase #2 $64.90   13.291%   $73.5259   $73.53   $73.55   $73.50  
  Purchase #3 $187.87   3.184%   $193.8518   $193.85   $193.85   $193.90  
  Purchase #4 $186.46   8.266%   $201.8728   $201.87   $201.85   $201.90  
  Purchase #5 $105.32   13.533%   $119.573   $119.57   $119.55   $119.60  
  Purchase #6 $128.76   11.509%   $143.579   $143.58   $143.60   $143.60  
  Purchase #7 $139.66   13.422%   $158.4052   $158.41   $158.40   $158.40  
  7 purchase totals = $865.88       $948.6108   $948.61   $948.60   $948.70