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 $67.35   10.868%   $74.6696   $74.67   $74.65   $74.70  
  Purchase #2 $231.69   8.353%   $251.0431   $251.04   $251.05   $251.00  
  Purchase #3 $5.77   6.456%   $6.1425   $6.14   $6.15   $6.10  
  Purchase #4 $41.40   3.628%   $42.902   $42.90   $42.90   $42.90  
  Purchase #5 $226.38   10.544%   $250.2495   $250.25   $250.25   $250.20  
  Purchase #6 $247.71   9.161%   $270.4027   $270.40   $270.40   $270.40  
  Purchase #7 $56.58   13.280%   $64.0938   $64.09   $64.10   $64.10  
  7 purchase totals = $876.88       $959.5032   $959.49   $959.50   $959.40