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 $95.54   6.423%   $101.6765   $101.68   $101.70   $101.70  
  Purchase #2 $242.90   11.155%   $269.9955   $270.00   $270.00   $270.00  
  Purchase #3 $15.60   5.840%   $16.511   $16.51   $16.50   $16.50  
  Purchase #4 $171.80   7.824%   $185.2416   $185.24   $185.25   $185.20  
  Purchase #5 $66.67   13.189%   $75.4631   $75.46   $75.45   $75.50  
  Purchase #6 $228.86   6.479%   $243.6878   $243.69   $243.70   $243.70  
  Purchase #7 $69.27   10.564%   $76.5877   $76.59   $76.60   $76.60  
  7 purchase totals = $890.64       $969.1632   $969.17   $969.20   $969.20