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 $214.68   3.128%   $221.3952   $221.40   $221.40   $221.40  
  Purchase #2 $45.75   5.347%   $48.1963   $48.20   $48.20   $48.20  
  Purchase #3 $54.89   4.104%   $57.1427   $57.14   $57.15   $57.10  
  Purchase #4 $125.78   5.246%   $132.3784   $132.38   $132.40   $132.40  
  Purchase #5 $201.31   10.630%   $222.7093   $222.71   $222.70   $222.70  
  Purchase #6 $175.96   3.724%   $182.5128   $182.51   $182.50   $182.50  
  Purchase #7 $119.54   9.169%   $130.5006   $130.50   $130.50   $130.50  
  7 purchase totals = $937.91       $994.8353   $994.84   $994.85   $994.80