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 $224.39   13.649%   $255.017   $255.02   $255.00   $255.00  
  Purchase #2 $23.34   11.271%   $25.9707   $25.97   $25.95   $26.00  
  Purchase #3 $16.92   11.218%   $18.8181   $18.82   $18.80   $18.80  
  Purchase #4 $74.87   11.423%   $83.4224   $83.42   $83.40   $83.40  
  Purchase #5 $95.97   5.324%   $101.0794   $101.08   $101.10   $101.10  
  Purchase #6 $95.83   3.766%   $99.439   $99.44   $99.45   $99.40  
  Purchase #7 $246.72   7.799%   $265.9617   $265.96   $265.95   $266.00  
  7 purchase totals = $778.04       $849.7083   $849.71   $849.65   $849.70