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 $231.68   12.786%   $261.3026   $261.30   $261.30   $261.30  
  Purchase #2 $60.32   4.381%   $62.9626   $62.96   $62.95   $63.00  
  Purchase #3 $129.78   3.672%   $134.5455   $134.55   $134.55   $134.50  
  Purchase #4 $175.58   3.316%   $181.4022   $181.40   $181.40   $181.40  
  Purchase #5 $27.58   13.859%   $31.4023   $31.40   $31.40   $31.40  
  Purchase #6 $10.79   7.551%   $11.6048   $11.60   $11.60   $11.60  
  Purchase #7 $153.74   8.269%   $166.4528   $166.45   $166.45   $166.50  
  7 purchase totals = $789.47       $849.6728   $849.66   $849.65   $849.70