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 $74.94   10.433%   $82.7585   $82.76   $82.75   $82.80  
  Purchase #2 $226.29   9.873%   $248.6316   $248.63   $248.65   $248.60  
  Purchase #3 $182.44   11.757%   $203.8895   $203.89   $203.90   $203.90  
  Purchase #4 $53.56   4.612%   $56.0302   $56.03   $56.05   $56.00  
  Purchase #5 $190.86   9.491%   $208.9745   $208.97   $208.95   $209.00  
  Purchase #6 $75.95   13.214%   $85.986   $85.99   $86.00   $86.00  
  Purchase #7 $224.72   7.739%   $242.1111   $242.11   $242.10   $242.10  
  7 purchase totals = $1,028.76       $1,128.3814   $1,128.38   $1,128.40   $1,128.40