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 $52.68   8.123%   $56.9592   $56.96   $56.95   $57.00  
  Purchase #2 $58.99   7.113%   $63.186   $63.19   $63.20   $63.20  
  Purchase #3 $173.49   7.777%   $186.9823   $186.98   $187.00   $187.00  
  Purchase #4 $49.81   6.363%   $52.9794   $52.98   $53.00   $53.00  
  Purchase #5 $107.81   11.535%   $120.2459   $120.25   $120.25   $120.20  
  Purchase #6 $242.35   4.383%   $252.9722   $252.97   $252.95   $253.00  
  Purchase #7 $185.27   3.300%   $191.3839   $191.38   $191.40   $191.40  
  7 purchase totals = $870.40       $924.7089   $924.71   $924.75   $924.80