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 $195.76   6.744%   $208.9621   $208.96   $208.95   $209.00  
  Purchase #2 $94.52   3.135%   $97.4832   $97.48   $97.50   $97.50  
  Purchase #3 $158.47   9.493%   $173.5136   $173.51   $173.50   $173.50  
  Purchase #4 $208.26   7.609%   $224.1065   $224.11   $224.10   $224.10  
  Purchase #5 $146.36   13.588%   $166.2474   $166.25   $166.25   $166.20  
  Purchase #6 $148.81   5.831%   $157.4871   $157.49   $157.50   $157.50  
  Purchase #7 $201.38   9.775%   $221.0649   $221.06   $221.05   $221.10  
  7 purchase totals = $1,153.56       $1,248.8648   $1,248.86   $1,248.85   $1,248.90