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 $67.53   8.341%   $73.1627   $73.16   $73.15   $73.20  
  Purchase #2 $97.50   9.787%   $107.0423   $107.04   $107.05   $107.00  
  Purchase #3 $72.89   13.604%   $82.806   $82.81   $82.80   $82.80  
  Purchase #4 $38.36   10.859%   $42.5255   $42.53   $42.55   $42.50  
  Purchase #5 $185.89   6.471%   $197.9189   $197.92   $197.90   $197.90  
  Purchase #6 $219.98   3.643%   $227.9939   $227.99   $228.00   $228.00  
  Purchase #7 $201.48   13.785%   $229.254   $229.25   $229.25   $229.30  
  7 purchase totals = $883.63       $960.7033   $960.70   $960.70   $960.70