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 $114.61   12.774%   $129.2503   $129.25   $129.25   $129.30  
  Purchase #2 $196.85   7.479%   $211.5724   $211.57   $211.55   $211.60  
  Purchase #3 $124.29   5.154%   $130.6959   $130.70   $130.70   $130.70  
  Purchase #4 $9.76   12.755%   $11.0049   $11.00   $11.00   $11.00  
  Purchase #5 $80.49   13.725%   $91.5373   $91.54   $91.55   $91.50  
  Purchase #6 $175.56   5.373%   $184.9928   $184.99   $185.00   $185.00  
  Purchase #7 $216.85   10.771%   $240.2069   $240.21   $240.20   $240.20  
  7 purchase totals = $918.41       $999.2605   $999.26   $999.25   $999.30