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 $243.26   4.248%   $253.5937   $253.59   $253.60   $253.60  
  Purchase #2 $54.87   9.195%   $59.9153   $59.92   $59.90   $59.90  
  Purchase #3 $32.95   3.386%   $34.0657   $34.07   $34.05   $34.10  
  Purchase #4 $105.30   8.358%   $114.101   $114.10   $114.10   $114.10  
  Purchase #5 $101.73   7.404%   $109.2621   $109.26   $109.25   $109.30  
  Purchase #6 $183.87   8.775%   $200.0046   $200.00   $200.00   $200.00  
  Purchase #7 $33.37   8.154%   $36.091   $36.09   $36.10   $36.10  
  7 purchase totals = $755.35       $807.0334   $807.03   $807.00   $807.10