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 $46.36   12.814%   $52.3006   $52.30   $52.30   $52.30  
  Purchase #2 $127.95   6.357%   $136.0838   $136.08   $136.10   $136.10  
  Purchase #3 $167.70   5.203%   $176.4254   $176.43   $176.45   $176.40  
  Purchase #4 $207.61   10.544%   $229.5004   $229.50   $229.50   $229.50  
  Purchase #5 $225.43   10.871%   $249.9365   $249.94   $249.95   $249.90  
  Purchase #6 $208.81   12.173%   $234.2284   $234.23   $234.25   $234.20  
  Purchase #7 $122.99   11.719%   $137.4032   $137.40   $137.40   $137.40  
  7 purchase totals = $1,106.85       $1,215.8783   $1,215.88   $1,215.95   $1,215.80