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 $59.55   5.861%   $63.0402   $63.04   $63.05   $63.00  
  Purchase #2 $44.99   9.118%   $49.0922   $49.09   $49.10   $49.10  
  Purchase #3 $174.29   10.438%   $192.4824   $192.48   $192.50   $192.50  
  Purchase #4 $93.34   8.478%   $101.2534   $101.25   $101.25   $101.30  
  Purchase #5 $107.67   7.304%   $115.5342   $115.53   $115.55   $115.50  
  Purchase #6 $247.57   11.326%   $275.6098   $275.61   $275.60   $275.60  
  Purchase #7 $185.66   6.681%   $198.0639   $198.06   $198.05   $198.10  
  7 purchase totals = $913.07       $995.0761   $995.06   $995.10   $995.10