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 $197.57   13.652%   $224.5423   $224.54   $224.55   $224.50  
  Purchase #2 $249.31   4.488%   $260.499   $260.50   $260.50   $260.50  
  Purchase #3 $110.57   11.509%   $123.2955   $123.30   $123.30   $123.30  
  Purchase #4 $88.61   9.282%   $96.8348   $96.83   $96.85   $96.80  
  Purchase #5 $228.76   3.289%   $236.2839   $236.28   $236.30   $236.30  
  Purchase #6 $139.53   11.231%   $155.2006   $155.20   $155.20   $155.20  
  Purchase #7 $245.88   8.150%   $265.9192   $265.92   $265.90   $265.90  
  7 purchase totals = $1,260.23       $1,362.5753   $1,362.57   $1,362.60   $1,362.50