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 $217.48   8.263%   $235.4504   $235.45   $235.45   $235.50  
  Purchase #2 $245.85   9.285%   $268.6772   $268.68   $268.70   $268.70  
  Purchase #3 $161.45   5.192%   $169.8325   $169.83   $169.85   $169.80  
  Purchase #4 $217.35   7.176%   $232.947   $232.95   $232.95   $232.90  
  Purchase #5 $82.53   12.552%   $92.8892   $92.89   $92.90   $92.90  
  Purchase #6 $215.89   3.868%   $224.2406   $224.24   $224.25   $224.20  
  Purchase #7 $119.68   8.314%   $129.6302   $129.63   $129.65   $129.60  
  7 purchase totals = $1,260.23       $1,353.6671   $1,353.67   $1,353.75   $1,353.60