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 $26.97   11.301%   $30.0179   $30.02   $30.00   $30.00  
  Purchase #2 $145.76   11.385%   $162.3548   $162.35   $162.35   $162.40  
  Purchase #3 $61.42   5.808%   $64.9873   $64.99   $65.00   $65.00  
  Purchase #4 $241.58   10.676%   $267.3711   $267.37   $267.35   $267.40  
  Purchase #5 $191.72   8.720%   $208.438   $208.44   $208.45   $208.40  
  Purchase #6 $126.86   10.623%   $140.3363   $140.34   $140.35   $140.30  
  Purchase #7 $125.48   11.646%   $140.0934   $140.09   $140.10   $140.10  
  7 purchase totals = $919.79       $1,013.5988   $1,013.60   $1,013.60   $1,013.60