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 $71.39   7.321%   $76.6165   $76.62   $76.60   $76.60  
  Purchase #2 $185.89   4.166%   $193.6342   $193.63   $193.65   $193.60  
  Purchase #3 $94.95   12.452%   $106.7732   $106.77   $106.75   $106.80  
  Purchase #4 $15.95   3.149%   $16.4523   $16.45   $16.45   $16.50  
  Purchase #5 $96.76   8.857%   $105.33   $105.33   $105.35   $105.30  
  Purchase #6 $34.92   10.834%   $38.7032   $38.70   $38.70   $38.70  
  Purchase #7 $164.98   7.257%   $176.9526   $176.95   $176.95   $177.00  
  7 purchase totals = $664.84       $714.4620   $714.45   $714.45   $714.50