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 $208.93   8.290%   $226.2503   $226.25   $226.25   $226.30  
  Purchase #2 $22.36   10.489%   $24.7053   $24.71   $24.70   $24.70  
  Purchase #3 $70.72   3.186%   $72.9731   $72.97   $72.95   $73.00  
  Purchase #4 $89.41   4.583%   $93.5077   $93.51   $93.50   $93.50  
  Purchase #5 $26.81   7.583%   $28.843   $28.84   $28.85   $28.80  
  Purchase #6 $151.41   13.515%   $171.8731   $171.87   $171.85   $171.90  
  Purchase #7 $146.81   8.744%   $159.6471   $159.65   $159.65   $159.60  
  7 purchase totals = $716.45       $777.7996   $777.80   $777.75   $777.80