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 $172.76   11.860%   $193.2493   $193.25   $193.25   $193.20  
  Purchase #2 $113.76   13.572%   $129.1995   $129.20   $129.20   $129.20  
  Purchase #3 $183.99   13.149%   $208.1828   $208.18   $208.20   $208.20  
  Purchase #4 $168.68   5.217%   $177.48   $177.48   $177.50   $177.50  
  Purchase #5 $211.61   11.621%   $236.2012   $236.20   $236.20   $236.20  
  Purchase #6 $236.69   13.174%   $267.8715   $267.87   $267.85   $267.90  
  Purchase #7 $104.85   11.672%   $117.0881   $117.09   $117.10   $117.10  
  7 purchase totals = $1,192.34       $1,329.2724   $1,329.27   $1,329.30   $1,329.30