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 $190.45   9.222%   $208.0133   $208.01   $208.00   $208.00  
  Purchase #2 $96.70   6.722%   $103.2002   $103.20   $103.20   $103.20  
  Purchase #3 $15.32   7.607%   $16.4854   $16.49   $16.50   $16.50  
  Purchase #4 $126.62   3.138%   $130.5933   $130.59   $130.60   $130.60  
  Purchase #5 $49.87   8.140%   $53.9294   $53.93   $53.95   $53.90  
  Purchase #6 $234.63   10.676%   $259.6791   $259.68   $259.70   $259.70  
  Purchase #7 $116.41   9.162%   $127.0755   $127.08   $127.10   $127.10  
  7 purchase totals = $830.00       $898.9762   $898.98   $899.05   $899.00