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 $51.65   10.717%   $57.1853   $57.19   $57.20   $57.20  
  Purchase #2 $215.59   11.147%   $239.6218   $239.62   $239.60   $239.60  
  Purchase #3 $60.67   3.197%   $62.6096   $62.61   $62.60   $62.60  
  Purchase #4 $65.55   13.239%   $74.2282   $74.23   $74.25   $74.20  
  Purchase #5 $131.71   7.138%   $141.1115   $141.11   $141.10   $141.10  
  Purchase #6 $200.25   7.465%   $215.1987   $215.20   $215.20   $215.20  
  Purchase #7 $146.42   12.448%   $164.6464   $164.65   $164.65   $164.60  
  7 purchase totals = $871.84       $954.6015   $954.61   $954.60   $954.50