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 $62.37   10.866%   $69.1471   $69.15   $69.15   $69.10  
  Purchase #2 $127.44   5.205%   $134.0733   $134.07   $134.05   $134.10  
  Purchase #3 $232.59   3.154%   $239.9259   $239.93   $239.95   $239.90  
  Purchase #4 $32.82   5.459%   $34.6116   $34.61   $34.60   $34.60  
  Purchase #5 $97.36   9.302%   $106.4164   $106.42   $106.40   $106.40  
  Purchase #6 $224.37   10.733%   $248.4516   $248.45   $248.45   $248.50  
  Purchase #7 $43.76   11.837%   $48.9399   $48.94   $48.95   $48.90  
  7 purchase totals = $820.71       $881.5658   $881.57   $881.55   $881.50