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 $56.45   8.557%   $61.2804   $61.28   $61.30   $61.30  
  Purchase #2 $232.66   7.449%   $249.9908   $249.99   $250.00   $250.00  
  Purchase #3 $119.99   13.392%   $136.0591   $136.06   $136.05   $136.10  
  Purchase #4 $178.89   13.380%   $202.8255   $202.83   $202.85   $202.80  
  Purchase #5 $6.69   3.433%   $6.9197   $6.92   $6.90   $6.90  
  Purchase #6 $32.68   8.699%   $35.5228   $35.52   $35.50   $35.50  
  Purchase #7 $239.57   6.292%   $254.6437   $254.64   $254.65   $254.60  
  7 purchase totals = $866.93       $947.2420   $947.24   $947.25   $947.20