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 $64.25   5.681%   $67.9   $67.90   $67.90   $67.90  
  Purchase #2 $173.68   11.460%   $193.5837   $193.58   $193.60   $193.60  
  Purchase #3 $75.92   4.792%   $79.5581   $79.56   $79.55   $79.60  
  Purchase #4 $245.79   9.659%   $269.5309   $269.53   $269.55   $269.50  
  Purchase #5 $250.97   12.623%   $282.6499   $282.65   $282.65   $282.60  
  Purchase #6 $76.50   3.149%   $78.909   $78.91   $78.90   $78.90  
  Purchase #7 $217.95   13.273%   $246.8785   $246.88   $246.90   $246.90  
  7 purchase totals = $1,105.06       $1,219.0101   $1,219.01   $1,219.05   $1,219.00