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 $39.83   12.135%   $44.6634   $44.66   $44.65   $44.70  
  Purchase #2 $202.71   6.396%   $215.6753   $215.68   $215.70   $215.70  
  Purchase #3 $215.89   7.685%   $232.4811   $232.48   $232.50   $232.50  
  Purchase #4 $208.49   7.548%   $224.2268   $224.23   $224.25   $224.20  
  Purchase #5 $96.58   7.802%   $104.1152   $104.12   $104.10   $104.10  
  Purchase #6 $246.41   13.797%   $280.4072   $280.41   $280.40   $280.40  
  Purchase #7 $239.84   3.688%   $248.6853   $248.69   $248.70   $248.70  
  7 purchase totals = $1,249.75       $1,350.2543   $1,350.27   $1,350.30   $1,350.30