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 $55.87   11.759%   $62.4398   $62.44   $62.45   $62.40  
  Purchase #2 $193.94   10.405%   $214.1195   $214.12   $214.10   $214.10  
  Purchase #3 $20.47   4.358%   $21.3621   $21.36   $21.35   $21.40  
  Purchase #4 $226.57   9.486%   $248.0624   $248.06   $248.05   $248.10  
  Purchase #5 $147.35   7.800%   $158.8433   $158.84   $158.85   $158.80  
  Purchase #6 $134.48   13.376%   $152.468   $152.47   $152.45   $152.50  
  Purchase #7 $55.25   12.293%   $62.0419   $62.04   $62.05   $62.00  
  7 purchase totals = $833.93       $919.3370   $919.33   $919.30   $919.30