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 $224.66   12.178%   $252.0191   $252.02   $252.00   $252.00  
  Purchase #2 $96.61   7.600%   $103.9524   $103.95   $103.95   $104.00  
  Purchase #3 $10.80   13.245%   $12.2305   $12.23   $12.25   $12.20  
  Purchase #4 $26.93   13.796%   $30.6453   $30.65   $30.65   $30.60  
  Purchase #5 $137.77   4.627%   $144.1446   $144.14   $144.15   $144.10  
  Purchase #6 $53.33   5.660%   $56.3485   $56.35   $56.35   $56.30  
  Purchase #7 $177.85   10.687%   $196.8568   $196.86   $196.85   $196.90  
  7 purchase totals = $727.95       $796.1972   $796.20   $796.20   $796.10