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 $241.44   11.400%   $268.9642   $268.96   $268.95   $269.00  
  Purchase #2 $167.92   10.490%   $185.5348   $185.53   $185.55   $185.50  
  Purchase #3 $233.55   3.482%   $241.6822   $241.68   $241.70   $241.70  
  Purchase #4 $182.27   13.517%   $206.9074   $206.91   $206.90   $206.90  
  Purchase #5 $121.69   11.467%   $135.6442   $135.64   $135.65   $135.60  
  Purchase #6 $102.37   4.785%   $107.2684   $107.27   $107.25   $107.30  
  Purchase #7 $224.71   10.145%   $247.5068   $247.51   $247.50   $247.50  
  7 purchase totals = $1,273.95       $1,393.5080   $1,393.50   $1,393.50   $1,393.50