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 $96.82   4.665%   $101.3367   $101.34   $101.35   $101.30  
  Purchase #2 $234.84   11.554%   $261.9734   $261.97   $261.95   $262.00  
  Purchase #3 $16.94   8.791%   $18.4292   $18.43   $18.45   $18.40  
  Purchase #4 $156.99   7.397%   $168.6026   $168.60   $168.60   $168.60  
  Purchase #5 $34.93   9.315%   $38.1837   $38.18   $38.20   $38.20  
  Purchase #6 $248.46   13.751%   $282.6257   $282.63   $282.65   $282.60  
  Purchase #7 $87.63   6.252%   $93.1086   $93.11   $93.10   $93.10  
  7 purchase totals = $876.61       $964.2599   $964.26   $964.30   $964.20