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 $242.75   7.657%   $261.3374   $261.34   $261.35   $261.30  
  Purchase #2 $148.91   8.552%   $161.6448   $161.64   $161.65   $161.60  
  Purchase #3 $21.64   10.863%   $23.9908   $23.99   $24.00   $24.00  
  Purchase #4 $40.72   4.136%   $42.4042   $42.40   $42.40   $42.40  
  Purchase #5 $196.30   8.263%   $212.5203   $212.52   $212.50   $212.50  
  Purchase #6 $208.40   11.262%   $231.87   $231.87   $231.85   $231.90  
  Purchase #7 $134.56   7.147%   $144.177   $144.18   $144.20   $144.20  
  7 purchase totals = $993.28       $1,077.9445   $1,077.94   $1,077.95   $1,077.90