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 $68.85   11.609%   $76.8428   $76.84   $76.85   $76.80  
  Purchase #2 $109.74   11.797%   $122.686   $122.69   $122.70   $122.70  
  Purchase #3 $168.58   12.581%   $189.789   $189.79   $189.80   $189.80  
  Purchase #4 $199.31   3.761%   $206.806   $206.81   $206.80   $206.80  
  Purchase #5 $124.83   10.135%   $137.4815   $137.48   $137.50   $137.50  
  Purchase #6 $97.90   11.426%   $109.0861   $109.09   $109.10   $109.10  
  Purchase #7 $208.40   8.667%   $226.462   $226.46   $226.45   $226.50  
  7 purchase totals = $977.61       $1,069.1534   $1,069.16   $1,069.20   $1,069.20