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 $248.27   7.359%   $266.5402   $266.54   $266.55   $266.50  
  Purchase #2 $15.52   13.631%   $17.6355   $17.64   $17.65   $17.60  
  Purchase #3 $35.63   10.225%   $39.2732   $39.27   $39.25   $39.30  
  Purchase #4 $84.67   7.210%   $90.7747   $90.77   $90.75   $90.80  
  Purchase #5 $59.29   8.338%   $64.2336   $64.23   $64.25   $64.20  
  Purchase #6 $14.88   5.856%   $15.7514   $15.75   $15.75   $15.80  
  Purchase #7 $169.99   8.387%   $184.2471   $184.25   $184.25   $184.20  
  7 purchase totals = $628.25       $678.4557   $678.45   $678.45   $678.40