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 $84.87   13.194%   $96.0677   $96.07   $96.05   $96.10  
  Purchase #2 $183.57   10.557%   $202.9495   $202.95   $202.95   $202.90  
  Purchase #3 $104.86   4.646%   $109.7318   $109.73   $109.75   $109.70  
  Purchase #4 $144.81   4.781%   $151.7334   $151.73   $151.75   $151.70  
  Purchase #5 $137.77   6.145%   $146.236   $146.24   $146.25   $146.20  
  Purchase #6 $168.60   9.731%   $185.0065   $185.01   $185.00   $185.00  
  Purchase #7 $35.62   5.777%   $37.6778   $37.68   $37.70   $37.70  
  7 purchase totals = $860.10       $929.4027   $929.41   $929.45   $929.30