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 $201.46   3.228%   $207.9631   $207.96   $207.95   $208.00  
  Purchase #2 $114.95   10.619%   $127.1565   $127.16   $127.15   $127.20  
  Purchase #3 $49.76   5.302%   $52.3983   $52.40   $52.40   $52.40  
  Purchase #4 $70.66   8.473%   $76.647   $76.65   $76.65   $76.60  
  Purchase #5 $29.58   6.233%   $31.4237   $31.42   $31.40   $31.40  
  Purchase #6 $248.32   8.123%   $268.491   $268.49   $268.50   $268.50  
  Purchase #7 $6.31   7.399%   $6.7769   $6.78   $6.80   $6.80  
  7 purchase totals = $721.04       $770.8565   $770.86   $770.85   $770.90