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 $65.66   8.552%   $71.2752   $71.28   $71.30   $71.30  
  Purchase #2 $183.73   8.126%   $198.6599   $198.66   $198.65   $198.70  
  Purchase #3 $249.58   6.483%   $265.7603   $265.76   $265.75   $265.80  
  Purchase #4 $200.58   13.272%   $227.201   $227.20   $227.20   $227.20  
  Purchase #5 $97.40   13.550%   $110.5977   $110.60   $110.60   $110.60  
  Purchase #6 $97.45   13.274%   $110.3855   $110.39   $110.40   $110.40  
  Purchase #7 $213.41   5.216%   $224.5415   $224.54   $224.55   $224.50  
  7 purchase totals = $1,107.81       $1,208.4211   $1,208.43   $1,208.45   $1,208.50