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 $85.49   9.195%   $93.3508   $93.35   $93.35   $93.40  
  Purchase #2 $213.46   6.764%   $227.8984   $227.90   $227.90   $227.90  
  Purchase #3 $26.64   5.229%   $28.033   $28.03   $28.05   $28.00  
  Purchase #4 $77.43   8.491%   $84.0046   $84.00   $84.00   $84.00  
  Purchase #5 $220.70   12.486%   $248.2566   $248.26   $248.25   $248.30  
  Purchase #6 $36.36   5.176%   $38.242   $38.24   $38.25   $38.20  
  Purchase #7 $57.53   4.129%   $59.9054   $59.91   $59.90   $59.90  
  7 purchase totals = $717.61       $779.6908   $779.69   $779.70   $779.70