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 $167.90   11.143%   $186.6091   $186.61   $186.60   $186.60  
  Purchase #2 $222.75   5.626%   $235.2819   $235.28   $235.30   $235.30  
  Purchase #3 $40.81   11.664%   $45.5701   $45.57   $45.55   $45.60  
  Purchase #4 $226.99   3.338%   $234.5669   $234.57   $234.55   $234.60  
  Purchase #5 $185.31   11.699%   $206.9894   $206.99   $207.00   $207.00  
  Purchase #6 $198.42   4.865%   $208.0731   $208.07   $208.05   $208.10  
  Purchase #7 $108.70   7.617%   $116.9797   $116.98   $117.00   $117.00  
  7 purchase totals = $1,150.88       $1,234.0702   $1,234.07   $1,234.05   $1,234.20