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 $109.62   8.802%   $119.2688   $119.27   $119.25   $119.30  
  Purchase #2 $209.92   13.751%   $238.7861   $238.79   $238.80   $238.80  
  Purchase #3 $90.48   12.147%   $101.4706   $101.47   $101.45   $101.50  
  Purchase #4 $176.67   3.537%   $182.9188   $182.92   $182.90   $182.90  
  Purchase #5 $60.87   4.617%   $63.6804   $63.68   $63.70   $63.70  
  Purchase #6 $156.88   13.863%   $178.6283   $178.63   $178.65   $178.60  
  Purchase #7 $183.35   5.753%   $193.8981   $193.90   $193.90   $193.90  
  7 purchase totals = $987.79       $1,078.6511   $1,078.66   $1,078.65   $1,078.70