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 $192.69   8.452%   $208.9762   $208.98   $209.00   $209.00  
  Purchase #2 $41.78   5.831%   $44.2162   $44.22   $44.20   $44.20  
  Purchase #3 $119.48   13.730%   $135.8846   $135.88   $135.90   $135.90  
  Purchase #4 $72.75   5.306%   $76.6101   $76.61   $76.60   $76.60  
  Purchase #5 $128.80   9.860%   $141.4997   $141.50   $141.50   $141.50  
  Purchase #6 $163.26   13.359%   $185.0699   $185.07   $185.05   $185.10  
  Purchase #7 $242.96   5.228%   $255.6619   $255.66   $255.65   $255.70  
  7 purchase totals = $961.72       $1,047.9186   $1,047.92   $1,047.90   $1,048.00