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 $23.83   11.308%   $26.5247   $26.52   $26.50   $26.50  
  Purchase #2 $177.48   3.336%   $183.4007   $183.40   $183.40   $183.40  
  Purchase #3 $31.73   6.278%   $33.722   $33.72   $33.70   $33.70  
  Purchase #4 $24.55   8.735%   $26.6944   $26.69   $26.70   $26.70  
  Purchase #5 $236.78   5.268%   $249.2536   $249.25   $249.25   $249.30  
  Purchase #6 $106.85   6.193%   $113.4672   $113.47   $113.45   $113.50  
  Purchase #7 $76.77   8.406%   $83.2233   $83.22   $83.20   $83.20  
  7 purchase totals = $677.99       $716.2859   $716.27   $716.20   $716.30