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 $68.84   10.798%   $76.2733   $76.27   $76.25   $76.30  
  Purchase #2 $224.51   11.229%   $249.7202   $249.72   $249.70   $249.70  
  Purchase #3 $46.57   11.757%   $52.0452   $52.05   $52.05   $52.00  
  Purchase #4 $180.35   13.105%   $203.9849   $203.98   $204.00   $204.00  
  Purchase #5 $18.61   13.383%   $21.1006   $21.10   $21.10   $21.10  
  Purchase #6 $137.94   13.169%   $156.1053   $156.11   $156.10   $156.10  
  Purchase #7 $54.49   13.771%   $61.9938   $61.99   $62.00   $62.00  
  7 purchase totals = $731.31       $821.2233   $821.22   $821.20   $821.20