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 $226.27   13.715%   $257.3029   $257.30   $257.30   $257.30  
  Purchase #2 $235.64   7.384%   $253.0397   $253.04   $253.05   $253.00  
  Purchase #3 $107.91   4.789%   $113.0778   $113.08   $113.10   $113.10  
  Purchase #4 $52.88   13.517%   $60.0278   $60.03   $60.05   $60.00  
  Purchase #5 $130.57   4.529%   $136.4835   $136.48   $136.50   $136.50  
  Purchase #6 $236.97   4.749%   $248.2237   $248.22   $248.20   $248.20  
  Purchase #7 $112.97   8.127%   $122.1511   $122.15   $122.15   $122.20  
  7 purchase totals = $1,103.21       $1,190.3065   $1,190.30   $1,190.35   $1,190.30