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 $66.95   7.502%   $71.9726   $71.97   $71.95   $72.00  
  Purchase #2 $244.43   8.181%   $264.4268   $264.43   $264.45   $264.40  
  Purchase #3 $140.93   5.426%   $148.5769   $148.58   $148.60   $148.60  
  Purchase #4 $86.75   13.283%   $98.273   $98.27   $98.25   $98.30  
  Purchase #5 $130.68   13.243%   $147.986   $147.99   $148.00   $148.00  
  Purchase #6 $218.83   9.452%   $239.5138   $239.51   $239.50   $239.50  
  Purchase #7 $15.71   3.390%   $16.2426   $16.24   $16.25   $16.20  
  7 purchase totals = $904.28       $986.9917   $986.99   $987.00   $987.00