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 $228.68   9.208%   $249.7369   $249.74   $249.75   $249.70  
  Purchase #2 $61.88   5.707%   $65.4115   $65.41   $65.40   $65.40  
  Purchase #3 $87.63   3.649%   $90.8276   $90.83   $90.85   $90.80  
  Purchase #4 $38.80   4.246%   $40.4474   $40.45   $40.45   $40.40  
  Purchase #5 $194.48   6.869%   $207.8388   $207.84   $207.85   $207.80  
  Purchase #6 $68.71   13.839%   $78.2188   $78.22   $78.20   $78.20  
  Purchase #7 $23.84   12.230%   $26.7556   $26.76   $26.75   $26.80  
  7 purchase totals = $704.02       $759.2366   $759.25   $759.25   $759.10