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 $246.63   11.157%   $274.1465   $274.15   $274.15   $274.10  
  Purchase #2 $79.82   8.282%   $86.4307   $86.43   $86.45   $86.40  
  Purchase #3 $105.56   10.836%   $116.9985   $117.00   $117.00   $117.00  
  Purchase #4 $7.89   12.254%   $8.8568   $8.86   $8.85   $8.90  
  Purchase #5 $52.28   5.116%   $54.9546   $54.95   $54.95   $55.00  
  Purchase #6 $49.73   3.566%   $51.5034   $51.50   $51.50   $51.50  
  Purchase #7 $202.77   9.553%   $222.1406   $222.14   $222.15   $222.10  
  7 purchase totals = $744.68       $815.0311   $815.03   $815.05   $815.00