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 $208.59   5.660%   $220.3962   $220.40   $220.40   $220.40  
  Purchase #2 $195.98   11.702%   $218.9136   $218.91   $218.90   $218.90  
  Purchase #3 $55.91   13.667%   $63.5512   $63.55   $63.55   $63.60  
  Purchase #4 $164.46   11.536%   $183.4321   $183.43   $183.45   $183.40  
  Purchase #5 $245.34   8.621%   $266.4908   $266.49   $266.50   $266.50  
  Purchase #6 $175.80   8.819%   $191.3038   $191.30   $191.30   $191.30  
  Purchase #7 $84.67   12.729%   $95.4476   $95.45   $95.45   $95.40  
  7 purchase totals = $1,130.75       $1,239.5353   $1,239.53   $1,239.55   $1,239.50