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 $14.46   5.842%   $15.3048   $15.30   $15.30   $15.30  
  Purchase #2 $211.65   13.223%   $239.6365   $239.64   $239.65   $239.60  
  Purchase #3 $162.76   8.789%   $177.065   $177.07   $177.05   $177.10  
  Purchase #4 $214.42   5.141%   $225.4433   $225.44   $225.45   $225.40  
  Purchase #5 $212.94   4.379%   $222.2646   $222.26   $222.25   $222.30  
  Purchase #6 $6.71   3.485%   $6.9438   $6.94   $6.95   $6.90  
  Purchase #7 $35.32   5.656%   $37.3177   $37.32   $37.30   $37.30  
  7 purchase totals = $858.26       $923.9757   $923.97   $923.95   $923.90