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 $208.42   12.393%   $234.2495   $234.25   $234.25   $234.20  
  Purchase #2 $64.39   9.419%   $70.4549   $70.45   $70.45   $70.50  
  Purchase #3 $135.99   10.705%   $150.5477   $150.55   $150.55   $150.50  
  Purchase #4 $139.45   8.695%   $151.5752   $151.58   $151.60   $151.60  
  Purchase #5 $68.43   8.630%   $74.3355   $74.34   $74.35   $74.30  
  Purchase #6 $35.69   13.405%   $40.4742   $40.47   $40.45   $40.50  
  Purchase #7 $65.34   7.105%   $69.9824   $69.98   $70.00   $70.00  
  7 purchase totals = $717.71       $791.6194   $791.62   $791.65   $791.60