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 $193.56   10.677%   $214.2264   $214.23   $214.25   $214.20  
  Purchase #2 $164.87   7.858%   $177.8255   $177.83   $177.85   $177.80  
  Purchase #3 $151.25   13.643%   $171.885   $171.89   $171.90   $171.90  
  Purchase #4 $109.62   7.153%   $117.4611   $117.46   $117.45   $117.50  
  Purchase #5 $208.58   12.462%   $234.5732   $234.57   $234.55   $234.60  
  Purchase #6 $53.76   5.476%   $56.7039   $56.70   $56.70   $56.70  
  Purchase #7 $218.95   8.342%   $237.2148   $237.21   $237.20   $237.20  
  7 purchase totals = $1,100.59       $1,209.8899   $1,209.89   $1,209.90   $1,209.90