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 $216.72   10.724%   $239.9611   $239.96   $239.95   $240.00  
  Purchase #2 $163.71   12.354%   $183.9347   $183.93   $183.95   $183.90  
  Purchase #3 $126.95   4.592%   $132.7795   $132.78   $132.80   $132.80  
  Purchase #4 $105.66   12.617%   $118.9911   $118.99   $119.00   $119.00  
  Purchase #5 $51.90   10.362%   $57.2779   $57.28   $57.30   $57.30  
  Purchase #6 $109.99   13.321%   $124.6418   $124.64   $124.65   $124.60  
  Purchase #7 $152.86   9.464%   $167.3267   $167.33   $167.35   $167.30  
  7 purchase totals = $927.79       $1,024.9128   $1,024.91   $1,025.00   $1,024.90