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 $56.68   11.563%   $63.2339   $63.23   $63.25   $63.20  
  Purchase #2 $151.86   3.327%   $156.9124   $156.91   $156.90   $156.90  
  Purchase #3 $18.83   7.628%   $20.2664   $20.27   $20.25   $20.30  
  Purchase #4 $58.62   4.105%   $61.0264   $61.03   $61.05   $61.00  
  Purchase #5 $65.62   5.489%   $69.2219   $69.22   $69.20   $69.20  
  Purchase #6 $54.40   10.512%   $60.1185   $60.12   $60.10   $60.10  
  Purchase #7 $52.26   10.687%   $57.845   $57.85   $57.85   $57.80  
  7 purchase totals = $458.27       $488.6245   $488.63   $488.60   $488.50