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 $112.39   8.670%   $122.1342   $122.13   $122.15   $122.10  
  Purchase #2 $194.54   12.376%   $218.6163   $218.62   $218.60   $218.60  
  Purchase #3 $161.76   13.393%   $183.4245   $183.42   $183.40   $183.40  
  Purchase #4 $54.71   8.212%   $59.2028   $59.20   $59.20   $59.20  
  Purchase #5 $14.85   11.240%   $16.5191   $16.52   $16.50   $16.50  
  Purchase #6 $81.77   3.102%   $84.3065   $84.31   $84.30   $84.30  
  Purchase #7 $235.70   13.449%   $267.3993   $267.40   $267.40   $267.40  
  7 purchase totals = $855.72       $951.6027   $951.60   $951.55   $951.50