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 $189.65   9.652%   $207.955   $207.96   $207.95   $208.00  
  Purchase #2 $90.26   10.688%   $99.907   $99.91   $99.90   $99.90  
  Purchase #3 $109.83   4.370%   $114.6296   $114.63   $114.65   $114.60  
  Purchase #4 $177.63   7.529%   $191.0038   $191.00   $191.00   $191.00  
  Purchase #5 $105.86   3.303%   $109.3566   $109.36   $109.35   $109.40  
  Purchase #6 $122.42   4.514%   $127.946   $127.95   $127.95   $127.90  
  Purchase #7 $76.60   6.263%   $81.3975   $81.40   $81.40   $81.40  
  7 purchase totals = $872.25       $932.1955   $932.21   $932.20   $932.20