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 $31.56   10.752%   $34.9533   $34.95   $34.95   $35.00  
  Purchase #2 $127.75   9.620%   $140.0396   $140.04   $140.05   $140.00  
  Purchase #3 $68.58   5.827%   $72.5762   $72.58   $72.60   $72.60  
  Purchase #4 $186.93   11.338%   $208.1241   $208.12   $208.10   $208.10  
  Purchase #5 $78.70   13.625%   $89.4229   $89.42   $89.40   $89.40  
  Purchase #6 $13.77   6.758%   $14.7006   $14.70   $14.70   $14.70  
  Purchase #7 $69.86   7.632%   $75.1917   $75.19   $75.20   $75.20  
  7 purchase totals = $577.15       $635.0084   $635.00   $635.00   $635.00