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 $86.68   11.553%   $96.6941   $96.69   $96.70   $96.70  
  Purchase #2 $164.87   7.752%   $177.6507   $177.65   $177.65   $177.70  
  Purchase #3 $115.62   11.117%   $128.4735   $128.47   $128.45   $128.50  
  Purchase #4 $21.76   13.735%   $24.7487   $24.75   $24.75   $24.70  
  Purchase #5 $141.28   11.448%   $157.4537   $157.45   $157.45   $157.50  
  Purchase #6 $249.56   9.256%   $272.6593   $272.66   $272.65   $272.70  
  Purchase #7 $141.55   11.305%   $157.5522   $157.55   $157.55   $157.60  
  7 purchase totals = $921.32       $1,015.2322   $1,015.22   $1,015.20   $1,015.40