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 $115.32   7.659%   $124.1524   $124.15   $124.15   $124.20  
  Purchase #2 $11.54   6.114%   $12.2456   $12.25   $12.25   $12.20  
  Purchase #3 $84.85   12.292%   $95.2798   $95.28   $95.30   $95.30  
  Purchase #4 $49.98   11.566%   $55.7607   $55.76   $55.75   $55.80  
  Purchase #5 $187.88   9.670%   $206.048   $206.05   $206.05   $206.00  
  Purchase #6 $200.90   10.686%   $222.3682   $222.37   $222.35   $222.40  
  Purchase #7 $250.85   7.168%   $268.8309   $268.83   $268.85   $268.80  
  7 purchase totals = $901.32       $984.6856   $984.69   $984.70   $984.70