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 $247.43   13.769%   $281.4986   $281.50   $281.50   $281.50  
  Purchase #2 $65.36   4.661%   $68.4064   $68.41   $68.40   $68.40  
  Purchase #3 $81.68   13.751%   $92.9118   $92.91   $92.90   $92.90  
  Purchase #4 $107.52   11.546%   $119.9343   $119.93   $119.95   $119.90  
  Purchase #5 $95.83   13.116%   $108.3991   $108.40   $108.40   $108.40  
  Purchase #6 $126.70   6.241%   $134.6073   $134.61   $134.60   $134.60  
  Purchase #7 $123.54   5.413%   $130.2272   $130.23   $130.25   $130.20  
  7 purchase totals = $848.06       $935.9847   $935.99   $936.00   $935.90