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 $203.37   10.484%   $224.6913   $224.69   $224.70   $224.70  
  Purchase #2 $80.29   7.432%   $86.2572   $86.26   $86.25   $86.30  
  Purchase #3 $240.83   13.754%   $273.9538   $273.95   $273.95   $274.00  
  Purchase #4 $108.62   3.690%   $112.6281   $112.63   $112.65   $112.60  
  Purchase #5 $237.50   11.686%   $265.2543   $265.25   $265.25   $265.30  
  Purchase #6 $208.60   13.860%   $237.512   $237.51   $237.50   $237.50  
  Purchase #7 $92.59   6.301%   $98.4241   $98.42   $98.40   $98.40  
  7 purchase totals = $1,171.80       $1,298.7208   $1,298.71   $1,298.70   $1,298.80