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 $53.45   11.537%   $59.6165   $59.62   $59.60   $59.60  
  Purchase #2 $24.61   5.738%   $26.0221   $26.02   $26.00   $26.00  
  Purchase #3 $60.25   11.593%   $67.2348   $67.23   $67.25   $67.20  
  Purchase #4 $76.25   4.199%   $79.4517   $79.45   $79.45   $79.50  
  Purchase #5 $192.68   8.228%   $208.5337   $208.53   $208.55   $208.50  
  Purchase #6 $167.59   13.228%   $189.7588   $189.76   $189.75   $189.80  
  Purchase #7 $188.85   7.424%   $202.8702   $202.87   $202.85   $202.90  
  7 purchase totals = $763.68       $833.4878   $833.48   $833.45   $833.50