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 $57.53   7.136%   $61.6353   $61.64   $61.65   $61.60  
  Purchase #2 $28.40   3.783%   $29.4744   $29.47   $29.45   $29.50  
  Purchase #3 $186.48   3.693%   $193.3667   $193.37   $193.35   $193.40  
  Purchase #4 $151.86   9.263%   $165.9268   $165.93   $165.95   $165.90  
  Purchase #5 $215.47   11.238%   $239.6845   $239.68   $239.70   $239.70  
  Purchase #6 $201.96   7.751%   $217.6139   $217.61   $217.60   $217.60  
  Purchase #7 $71.61   4.299%   $74.6885   $74.69   $74.70   $74.70  
  7 purchase totals = $913.31       $982.3901   $982.39   $982.40   $982.40