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 $207.50   9.556%   $227.3287   $227.33   $227.35   $227.30  
  Purchase #2 $53.54   12.159%   $60.0499   $60.05   $60.05   $60.00  
  Purchase #3 $68.96   13.629%   $78.3586   $78.36   $78.35   $78.40  
  Purchase #4 $15.78   9.147%   $17.2234   $17.22   $17.20   $17.20  
  Purchase #5 $163.65   7.862%   $176.5162   $176.52   $176.50   $176.50  
  Purchase #6 $136.32   8.863%   $148.402   $148.40   $148.40   $148.40  
  Purchase #7 $48.32   11.657%   $53.9527   $53.95   $53.95   $54.00  
  7 purchase totals = $694.07       $761.8315   $761.83   $761.80   $761.80