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 $33.62   9.203%   $36.714   $36.71   $36.70   $36.70  
  Purchase #2 $131.99   11.102%   $146.6435   $146.64   $146.65   $146.60  
  Purchase #3 $168.41   10.197%   $185.5828   $185.58   $185.60   $185.60  
  Purchase #4 $78.44   6.493%   $83.5331   $83.53   $83.55   $83.50  
  Purchase #5 $159.77   10.201%   $176.0681   $176.07   $176.05   $176.10  
  Purchase #6 $210.99   13.549%   $239.577   $239.58   $239.60   $239.60  
  Purchase #7 $218.81   11.691%   $244.3911   $244.39   $244.40   $244.40  
  7 purchase totals = $1,002.03       $1,112.5096   $1,112.50   $1,112.55   $1,112.50