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 $215.63   13.451%   $244.6344   $244.63   $244.65   $244.60  
  Purchase #2 $23.41   6.420%   $24.9129   $24.91   $24.90   $24.90  
  Purchase #3 $116.27   9.211%   $126.9796   $126.98   $127.00   $127.00  
  Purchase #4 $221.34   4.264%   $230.7779   $230.78   $230.80   $230.80  
  Purchase #5 $123.30   11.863%   $137.9271   $137.93   $137.95   $137.90  
  Purchase #6 $151.84   9.681%   $166.5396   $166.54   $166.55   $166.50  
  Purchase #7 $22.67   5.831%   $23.9919   $23.99   $24.00   $24.00  
  7 purchase totals = $874.46       $955.7634   $955.76   $955.85   $955.70