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 $174.73   12.322%   $196.2602   $196.26   $196.25   $196.30  
  Purchase #2 $223.91   11.633%   $249.9575   $249.96   $249.95   $250.00  
  Purchase #3 $15.52   12.684%   $17.4886   $17.49   $17.50   $17.50  
  Purchase #4 $175.76   13.455%   $199.4085   $199.41   $199.40   $199.40  
  Purchase #5 $60.71   9.542%   $66.5029   $66.50   $66.50   $66.50  
  Purchase #6 $151.59   7.539%   $163.0184   $163.02   $163.00   $163.00  
  Purchase #7 $10.69   5.186%   $11.2444   $11.24   $11.25   $11.20  
  7 purchase totals = $812.91       $903.8805   $903.88   $903.85   $903.90