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 $62.45   10.705%   $69.1353   $69.14   $69.15   $69.10  
  Purchase #2 $247.47   7.710%   $266.5499   $266.55   $266.55   $266.50  
  Purchase #3 $130.47   4.512%   $136.3568   $136.36   $136.35   $136.40  
  Purchase #4 $198.71   7.668%   $213.9471   $213.95   $213.95   $213.90  
  Purchase #5 $68.82   9.628%   $75.446   $75.45   $75.45   $75.40  
  Purchase #6 $239.81   3.386%   $247.93   $247.93   $247.95   $247.90  
  Purchase #7 $247.87   12.256%   $278.2489   $278.25   $278.25   $278.20  
  7 purchase totals = $1,195.60       $1,287.6140   $1,287.63   $1,287.65   $1,287.40