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 $30.85   13.320%   $34.9592   $34.96   $34.95   $35.00  
  Purchase #2 $166.26   9.857%   $182.6482   $182.65   $182.65   $182.60  
  Purchase #3 $220.51   13.794%   $250.9271   $250.93   $250.95   $250.90  
  Purchase #4 $212.46   13.797%   $241.7731   $241.77   $241.75   $241.80  
  Purchase #5 $140.54   4.586%   $146.9852   $146.99   $147.00   $147.00  
  Purchase #6 $16.57   5.358%   $17.4578   $17.46   $17.45   $17.50  
  Purchase #7 $103.35   8.630%   $112.2691   $112.27   $112.25   $112.30  
  7 purchase totals = $890.54       $987.0197   $987.03   $987.00   $987.10