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 $208.58   11.527%   $232.623   $232.62   $232.60   $232.60  
  Purchase #2 $66.54   12.482%   $74.8455   $74.85   $74.85   $74.80  
  Purchase #3 $189.93   12.770%   $214.1841   $214.18   $214.20   $214.20  
  Purchase #4 $35.99   7.146%   $38.5618   $38.56   $38.55   $38.60  
  Purchase #5 $111.68   3.455%   $115.5385   $115.54   $115.55   $115.50  
  Purchase #6 $113.76   4.427%   $118.7962   $118.80   $118.80   $118.80  
  Purchase #7 $138.60   13.326%   $157.0698   $157.07   $157.05   $157.10  
  7 purchase totals = $865.08       $951.6189   $951.62   $951.60   $951.60