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 $235.27   10.669%   $260.371   $260.37   $260.35   $260.40  
  Purchase #2 $114.81   3.575%   $118.9145   $118.91   $118.90   $118.90  
  Purchase #3 $111.88   13.491%   $126.9737   $126.97   $126.95   $127.00  
  Purchase #4 $184.85   12.725%   $208.3722   $208.37   $208.35   $208.40  
  Purchase #5 $29.58   3.651%   $30.66   $30.66   $30.65   $30.70  
  Purchase #6 $215.65   8.593%   $234.1808   $234.18   $234.20   $234.20  
  Purchase #7 $206.78   13.215%   $234.106   $234.11   $234.10   $234.10  
  7 purchase totals = $1,098.82       $1,213.5782   $1,213.57   $1,213.50   $1,213.70