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 $35.79   6.823%   $38.232   $38.23   $38.25   $38.20  
  Purchase #2 $106.33   8.575%   $115.4478   $115.45   $115.45   $115.40  
  Purchase #3 $108.98   5.151%   $114.5936   $114.59   $114.60   $114.60  
  Purchase #4 $235.63   11.408%   $262.5107   $262.51   $262.50   $262.50  
  Purchase #5 $38.74   5.859%   $41.0098   $41.01   $41.00   $41.00  
  Purchase #6 $180.89   9.584%   $198.2265   $198.23   $198.25   $198.20  
  Purchase #7 $82.55   11.291%   $91.8707   $91.87   $91.85   $91.90  
  7 purchase totals = $788.91       $861.8911   $861.89   $861.90   $861.80