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 $57.59   13.143%   $65.1591   $65.16   $65.15   $65.20  
  Purchase #2 $206.63   8.566%   $224.3299   $224.33   $224.35   $224.30  
  Purchase #3 $169.56   9.689%   $185.9887   $185.99   $186.00   $186.00  
  Purchase #4 $161.41   12.867%   $182.1786   $182.18   $182.20   $182.20  
  Purchase #5 $40.92   8.105%   $44.2366   $44.24   $44.25   $44.20  
  Purchase #6 $47.48   9.239%   $51.8667   $51.87   $51.85   $51.90  
  Purchase #7 $67.61   7.769%   $72.8626   $72.86   $72.85   $72.90  
  7 purchase totals = $751.20       $826.6222   $826.63   $826.65   $826.70