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 $199.53   13.520%   $226.5065   $226.51   $226.50   $226.50  
  Purchase #2 $231.97   12.620%   $261.2446   $261.24   $261.25   $261.20  
  Purchase #3 $230.37   9.587%   $252.4556   $252.46   $252.45   $252.50  
  Purchase #4 $230.52   10.521%   $254.773   $254.77   $254.75   $254.80  
  Purchase #5 $184.89   12.131%   $207.319   $207.32   $207.30   $207.30  
  Purchase #6 $52.30   7.592%   $56.2706   $56.27   $56.25   $56.30  
  Purchase #7 $245.35   5.406%   $258.6136   $258.61   $258.60   $258.60  
  7 purchase totals = $1,374.93       $1,517.1829   $1,517.18   $1,517.10   $1,517.20