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 $187.95   7.171%   $201.4279   $201.43   $201.45   $201.40  
  Purchase #2 $54.75   5.683%   $57.8614   $57.86   $57.85   $57.90  
  Purchase #3 $200.93   13.105%   $227.2619   $227.26   $227.25   $227.30  
  Purchase #4 $153.92   12.452%   $173.0861   $173.09   $173.10   $173.10  
  Purchase #5 $129.59   8.799%   $140.9926   $140.99   $141.00   $141.00  
  Purchase #6 $209.91   5.845%   $222.1792   $222.18   $222.20   $222.20  
  Purchase #7 $58.41   3.809%   $60.6348   $60.63   $60.65   $60.60  
  7 purchase totals = $995.46       $1,083.4439   $1,083.44   $1,083.50   $1,083.50