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 $109.82   8.853%   $119.5424   $119.54   $119.55   $119.50  
  Purchase #2 $243.79   3.759%   $252.9541   $252.95   $252.95   $253.00  
  Purchase #3 $134.58   3.734%   $139.6052   $139.61   $139.60   $139.60  
  Purchase #4 $201.31   11.298%   $224.054   $224.05   $224.05   $224.10  
  Purchase #5 $239.46   13.543%   $271.8901   $271.89   $271.90   $271.90  
  Purchase #6 $124.81   13.138%   $141.2075   $141.21   $141.20   $141.20  
  Purchase #7 $97.50   12.201%   $109.396   $109.40   $109.40   $109.40  
  7 purchase totals = $1,151.27       $1,258.6493   $1,258.65   $1,258.65   $1,258.70