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 $60.40   8.528%   $65.5509   $65.55   $65.55   $65.60  
  Purchase #2 $222.68   7.724%   $239.8798   $239.88   $239.90   $239.90  
  Purchase #3 $168.77   7.678%   $181.7282   $181.73   $181.75   $181.70  
  Purchase #4 $56.43   13.609%   $64.1096   $64.11   $64.10   $64.10  
  Purchase #5 $133.27   4.549%   $139.3325   $139.33   $139.35   $139.30  
  Purchase #6 $101.85   10.132%   $112.1694   $112.17   $112.15   $112.20  
  Purchase #7 $169.28   3.491%   $175.1896   $175.19   $175.20   $175.20  
  7 purchase totals = $912.68       $977.9600   $977.96   $978.00   $978.00