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 $185.41   6.210%   $196.924   $196.92   $196.90   $196.90  
  Purchase #2 $10.89   7.561%   $11.7134   $11.71   $11.70   $11.70  
  Purchase #3 $119.61   6.173%   $126.9935   $126.99   $127.00   $127.00  
  Purchase #4 $140.59   11.845%   $157.2429   $157.24   $157.25   $157.20  
  Purchase #5 $212.51   13.523%   $241.2477   $241.25   $241.25   $241.20  
  Purchase #6 $59.36   4.493%   $62.027   $62.03   $62.05   $62.00  
  Purchase #7 $211.95   9.652%   $232.4074   $232.41   $232.40   $232.40  
  7 purchase totals = $940.32       $1,028.5559   $1,028.55   $1,028.55   $1,028.40