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 $42.83   10.678%   $47.4034   $47.40   $47.40   $47.40  
  Purchase #2 $188.81   7.359%   $202.7045   $202.70   $202.70   $202.70  
  Purchase #3 $74.55   5.446%   $78.61   $78.61   $78.60   $78.60  
  Purchase #4 $145.55   4.462%   $152.0444   $152.04   $152.05   $152.00  
  Purchase #5 $235.46   6.752%   $251.3583   $251.36   $251.35   $251.40  
  Purchase #6 $8.25   4.249%   $8.6005   $8.60   $8.60   $8.60  
  Purchase #7 $193.70   11.147%   $215.2917   $215.29   $215.30   $215.30  
  7 purchase totals = $889.15       $956.0128   $956.00   $956.00   $956.00