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 $219.89   5.167%   $231.2517   $231.25   $231.25   $231.30  
  Purchase #2 $189.39   12.666%   $213.3781   $213.38   $213.40   $213.40  
  Purchase #3 $154.62   7.757%   $166.6139   $166.61   $166.60   $166.60  
  Purchase #4 $13.66   5.279%   $14.3811   $14.38   $14.40   $14.40  
  Purchase #5 $125.89   7.614%   $135.4753   $135.48   $135.50   $135.50  
  Purchase #6 $241.37   11.653%   $269.4968   $269.50   $269.50   $269.50  
  Purchase #7 $61.81   11.492%   $68.9132   $68.91   $68.90   $68.90  
  7 purchase totals = $1,006.63       $1,099.5101   $1,099.51   $1,099.55   $1,099.60