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 $173.68   13.384%   $196.9253   $196.93   $196.95   $196.90  
  Purchase #2 $140.55   11.115%   $156.1721   $156.17   $156.15   $156.20  
  Purchase #3 $69.32   7.158%   $74.2819   $74.28   $74.30   $74.30  
  Purchase #4 $202.27   3.325%   $208.9955   $209.00   $209.00   $209.00  
  Purchase #5 $147.49   11.724%   $164.7817   $164.78   $164.80   $164.80  
  Purchase #6 $156.93   11.763%   $175.3897   $175.39   $175.40   $175.40  
  Purchase #7 $213.76   9.832%   $234.7769   $234.78   $234.80   $234.80  
  7 purchase totals = $1,104.00       $1,211.3231   $1,211.33   $1,211.40   $1,211.40