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 $46.89   4.702%   $49.0948   $49.09   $49.10   $49.10  
  Purchase #2 $208.53   7.259%   $223.6672   $223.67   $223.65   $223.70  
  Purchase #3 $94.59   9.523%   $103.5978   $103.60   $103.60   $103.60  
  Purchase #4 $122.53   13.628%   $139.2284   $139.23   $139.25   $139.20  
  Purchase #5 $156.94   12.579%   $176.6815   $176.68   $176.70   $176.70  
  Purchase #6 $69.25   11.700%   $77.3523   $77.35   $77.35   $77.40  
  Purchase #7 $185.72   11.750%   $207.5421   $207.54   $207.55   $207.50  
  7 purchase totals = $884.45       $977.1641   $977.16   $977.20   $977.20