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 $24.28   10.490%   $26.827   $26.83   $26.85   $26.80  
  Purchase #2 $76.69   6.332%   $81.546   $81.55   $81.55   $81.50  
  Purchase #3 $62.34   6.787%   $66.571   $66.57   $66.55   $66.60  
  Purchase #4 $42.74   8.818%   $46.5088   $46.51   $46.50   $46.50  
  Purchase #5 $182.47   10.267%   $201.2042   $201.20   $201.20   $201.20  
  Purchase #6 $73.52   12.228%   $82.51   $82.51   $82.50   $82.50  
  Purchase #7 $51.38   9.576%   $56.3001   $56.30   $56.30   $56.30  
  7 purchase totals = $513.42       $561.4671   $561.47   $561.45   $561.40