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 $136.89   12.309%   $153.7398   $153.74   $153.75   $153.70  
  Purchase #2 $184.73   6.223%   $196.2257   $196.23   $196.25   $196.20  
  Purchase #3 $195.26   9.380%   $213.5754   $213.58   $213.60   $213.60  
  Purchase #4 $227.45   5.392%   $239.7141   $239.71   $239.70   $239.70  
  Purchase #5 $17.27   10.828%   $19.14   $19.14   $19.15   $19.10  
  Purchase #6 $111.41   11.769%   $124.5218   $124.52   $124.50   $124.50  
  Purchase #7 $207.58   4.436%   $216.7882   $216.79   $216.80   $216.80  
  7 purchase totals = $1,080.59       $1,163.7050   $1,163.71   $1,163.75   $1,163.60