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 $240.95   13.546%   $273.5891   $273.59   $273.60   $273.60  
  Purchase #2 $120.91   4.818%   $126.7354   $126.74   $126.75   $126.70  
  Purchase #3 $105.59   13.139%   $119.4635   $119.46   $119.45   $119.50  
  Purchase #4 $179.79   4.667%   $188.1808   $188.18   $188.20   $188.20  
  Purchase #5 $250.49   12.285%   $281.2627   $281.26   $281.25   $281.30  
  Purchase #6 $42.53   8.679%   $46.2212   $46.22   $46.20   $46.20  
  Purchase #7 $153.72   12.648%   $173.1625   $173.16   $173.15   $173.20  
  7 purchase totals = $1,093.98       $1,208.6152   $1,208.61   $1,208.60   $1,208.70