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 $235.82   5.848%   $249.6108   $249.61   $249.60   $249.60  
  Purchase #2 $141.51   11.283%   $157.4766   $157.48   $157.50   $157.50  
  Purchase #3 $117.75   11.627%   $131.4408   $131.44   $131.45   $131.40  
  Purchase #4 $91.39   3.636%   $94.7129   $94.71   $94.70   $94.70  
  Purchase #5 $94.51   10.565%   $104.495   $104.50   $104.50   $104.50  
  Purchase #6 $129.35   8.832%   $140.7742   $140.77   $140.75   $140.80  
  Purchase #7 $180.75   5.483%   $190.6605   $190.66   $190.65   $190.70  
  7 purchase totals = $991.08       $1,069.1708   $1,069.17   $1,069.15   $1,069.20