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 $84.82   9.186%   $92.6116   $92.61   $92.60   $92.60  
  Purchase #2 $148.31   7.637%   $159.6364   $159.64   $159.65   $159.60  
  Purchase #3 $130.91   10.404%   $144.5299   $144.53   $144.55   $144.50  
  Purchase #4 $73.68   5.800%   $77.9534   $77.95   $77.95   $78.00  
  Purchase #5 $238.49   9.220%   $260.4788   $260.48   $260.50   $260.50  
  Purchase #6 $169.49   9.587%   $185.739   $185.74   $185.75   $185.70  
  Purchase #7 $79.25   11.801%   $88.6023   $88.60   $88.60   $88.60  
  7 purchase totals = $924.95       $1,009.5514   $1,009.55   $1,009.60   $1,009.50