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 $26.86   10.614%   $29.7109   $29.71   $29.70   $29.70  
  Purchase #2 $109.55   8.296%   $118.6383   $118.64   $118.65   $118.60  
  Purchase #3 $53.71   8.459%   $58.2533   $58.25   $58.25   $58.30  
  Purchase #4 $214.59   6.157%   $227.8023   $227.80   $227.80   $227.80  
  Purchase #5 $136.68   11.234%   $152.0346   $152.03   $152.05   $152.00  
  Purchase #6 $176.43   6.752%   $188.3426   $188.34   $188.35   $188.30  
  Purchase #7 $183.83   5.328%   $193.6245   $193.62   $193.60   $193.60  
  7 purchase totals = $901.65       $968.4065   $968.39   $968.40   $968.30