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 $222.49   13.423%   $252.3548   $252.35   $252.35   $252.40  
  Purchase #2 $231.73   10.268%   $255.524   $255.52   $255.50   $255.50  
  Purchase #3 $55.55   7.613%   $59.779   $59.78   $59.80   $59.80  
  Purchase #4 $66.81   9.642%   $73.2518   $73.25   $73.25   $73.30  
  Purchase #5 $196.55   12.426%   $220.9733   $220.97   $220.95   $221.00  
  Purchase #6 $24.78   5.852%   $26.2301   $26.23   $26.25   $26.20  
  Purchase #7 $54.71   12.162%   $61.3638   $61.36   $61.35   $61.40  
  7 purchase totals = $852.62       $949.4768   $949.46   $949.45   $949.60