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 $34.91   5.856%   $36.9543   $36.95   $36.95   $37.00  
  Purchase #2 $13.73   3.472%   $14.2067   $14.21   $14.20   $14.20  
  Purchase #3 $127.67   9.223%   $139.445   $139.45   $139.45   $139.40  
  Purchase #4 $146.67   7.228%   $157.2713   $157.27   $157.25   $157.30  
  Purchase #5 $242.85   4.262%   $253.2003   $253.20   $253.20   $253.20  
  Purchase #6 $25.81   5.149%   $27.139   $27.14   $27.15   $27.10  
  Purchase #7 $121.76   10.689%   $134.7749   $134.77   $134.75   $134.80  
  7 purchase totals = $713.40       $762.9915   $762.99   $762.95   $763.00