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 $178.99   3.689%   $185.5929   $185.59   $185.60   $185.60  
  Purchase #2 $15.26   8.106%   $16.497   $16.50   $16.50   $16.50  
  Purchase #3 $33.50   4.592%   $35.0383   $35.04   $35.05   $35.00  
  Purchase #4 $71.37   13.717%   $81.1598   $81.16   $81.15   $81.20  
  Purchase #5 $155.88   6.539%   $166.073   $166.07   $166.05   $166.10  
  Purchase #6 $150.88   5.542%   $159.2418   $159.24   $159.25   $159.20  
  Purchase #7 $81.60   13.195%   $92.3671   $92.37   $92.35   $92.40  
  7 purchase totals = $687.48       $735.9699   $735.97   $735.95   $736.00