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 $34.77   12.277%   $39.0387   $39.04   $39.05   $39.00  
  Purchase #2 $235.96   12.434%   $265.2993   $265.30   $265.30   $265.30  
  Purchase #3 $127.75   5.240%   $134.4441   $134.44   $134.45   $134.40  
  Purchase #4 $161.25   8.503%   $174.9611   $174.96   $174.95   $175.00  
  Purchase #5 $182.76   5.146%   $192.1648   $192.16   $192.15   $192.20  
  Purchase #6 $199.53   4.626%   $208.7603   $208.76   $208.75   $208.80  
  Purchase #7 $10.43   12.253%   $11.708   $11.71   $11.70   $11.70  
  7 purchase totals = $952.45       $1,026.3763   $1,026.37   $1,026.35   $1,026.40