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 $56.68   3.358%   $58.5833   $58.58   $58.60   $58.60  
  Purchase #2 $240.90   13.531%   $273.4962   $273.50   $273.50   $273.50  
  Purchase #3 $76.75   3.169%   $79.1822   $79.18   $79.20   $79.20  
  Purchase #4 $239.42   3.782%   $248.4749   $248.47   $248.45   $248.50  
  Purchase #5 $82.71   10.798%   $91.641   $91.64   $91.65   $91.60  
  Purchase #6 $170.55   13.137%   $192.9552   $192.96   $192.95   $193.00  
  Purchase #7 $71.67   9.752%   $78.6593   $78.66   $78.65   $78.70  
  7 purchase totals = $938.68       $1,022.9921   $1,022.99   $1,023.00   $1,023.10