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 $181.99   13.661%   $206.8517   $206.85   $206.85   $206.90  
  Purchase #2 $207.43   8.647%   $225.3665   $225.37   $225.35   $225.40  
  Purchase #3 $176.63   7.574%   $190.008   $190.01   $190.00   $190.00  
  Purchase #4 $141.61   7.266%   $151.8994   $151.90   $151.90   $151.90  
  Purchase #5 $171.59   9.608%   $188.0764   $188.08   $188.10   $188.10  
  Purchase #6 $246.75   4.382%   $257.5626   $257.56   $257.55   $257.60  
  Purchase #7 $113.65   8.763%   $123.6091   $123.61   $123.60   $123.60  
  7 purchase totals = $1,239.65       $1,343.3737   $1,343.38   $1,343.35   $1,343.50