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 $14.57   10.218%   $16.0588   $16.06   $16.05   $16.10  
  Purchase #2 $65.44   3.286%   $67.5904   $67.59   $67.60   $67.60  
  Purchase #3 $119.64   7.722%   $128.8786   $128.88   $128.90   $128.90  
  Purchase #4 $197.36   3.737%   $204.7353   $204.74   $204.75   $204.70  
  Purchase #5 $70.76   5.769%   $74.8421   $74.84   $74.85   $74.80  
  Purchase #6 $122.50   13.804%   $139.4099   $139.41   $139.40   $139.40  
  Purchase #7 $217.55   7.493%   $233.851   $233.85   $233.85   $233.90  
  7 purchase totals = $807.82       $865.3661   $865.37   $865.40   $865.40