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 $56.83   6.209%   $60.3586   $60.36   $60.35   $60.40  
  Purchase #2 $216.39   4.768%   $226.7075   $226.71   $226.70   $226.70  
  Purchase #3 $100.65   11.439%   $112.1634   $112.16   $112.15   $112.20  
  Purchase #4 $83.32   11.233%   $92.6793   $92.68   $92.70   $92.70  
  Purchase #5 $16.78   3.695%   $17.4   $17.40   $17.40   $17.40  
  Purchase #6 $186.35   10.133%   $205.2328   $205.23   $205.25   $205.20  
  Purchase #7 $66.68   6.173%   $70.7962   $70.80   $70.80   $70.80  
  7 purchase totals = $727.00       $785.3378   $785.34   $785.35   $785.40