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 $236.50   11.541%   $263.7945   $263.79   $263.80   $263.80  
  Purchase #2 $248.45   9.835%   $272.8851   $272.89   $272.90   $272.90  
  Purchase #3 $67.82   3.509%   $70.1998   $70.20   $70.20   $70.20  
  Purchase #4 $229.27   4.520%   $239.633   $239.63   $239.65   $239.60  
  Purchase #5 $131.66   6.807%   $140.6221   $140.62   $140.60   $140.60  
  Purchase #6 $231.75   8.873%   $252.3132   $252.31   $252.30   $252.30  
  Purchase #7 $238.98   12.777%   $269.5145   $269.51   $269.50   $269.50  
  7 purchase totals = $1,384.43       $1,508.9622   $1,508.95   $1,508.95   $1,508.90