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 $248.59   13.357%   $281.7942   $281.79   $281.80   $281.80  
  Purchase #2 $199.35   8.510%   $216.3147   $216.31   $216.30   $216.30  
  Purchase #3 $11.33   5.866%   $11.9946   $11.99   $12.00   $12.00  
  Purchase #4 $166.44   11.233%   $185.1362   $185.14   $185.15   $185.10  
  Purchase #5 $51.71   9.852%   $56.8045   $56.80   $56.80   $56.80  
  Purchase #6 $13.54   3.407%   $14.0013   $14.00   $14.00   $14.00  
  Purchase #7 $200.43   8.505%   $217.4766   $217.48   $217.50   $217.50  
  7 purchase totals = $891.39       $983.5221   $983.51   $983.55   $983.50