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 $38.77   7.557%   $41.6998   $41.70   $41.70   $41.70  
  Purchase #2 $224.93   7.270%   $241.2824   $241.28   $241.30   $241.30  
  Purchase #3 $84.54   7.291%   $90.7038   $90.70   $90.70   $90.70  
  Purchase #4 $50.67   3.749%   $52.5696   $52.57   $52.55   $52.60  
  Purchase #5 $178.46   13.550%   $202.6413   $202.64   $202.65   $202.60  
  Purchase #6 $178.65   3.792%   $185.4244   $185.42   $185.40   $185.40  
  Purchase #7 $65.30   8.176%   $70.6389   $70.64   $70.65   $70.60  
  7 purchase totals = $821.32       $884.9602   $884.95   $884.95   $884.90