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 $229.99   13.599%   $261.2663   $261.27   $261.25   $261.30  
  Purchase #2 $212.85   10.519%   $235.2397   $235.24   $235.25   $235.20  
  Purchase #3 $189.92   11.762%   $212.2584   $212.26   $212.25   $212.30  
  Purchase #4 $216.98   3.247%   $224.0253   $224.03   $224.05   $224.00  
  Purchase #5 $242.93   4.572%   $254.0368   $254.04   $254.05   $254.00  
  Purchase #6 $86.89   13.477%   $98.6002   $98.60   $98.60   $98.60  
  Purchase #7 $70.42   9.104%   $76.831   $76.83   $76.85   $76.80  
  7 purchase totals = $1,249.98       $1,362.2577   $1,362.27   $1,362.30   $1,362.20