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 $181.74   10.577%   $200.9626   $200.96   $200.95   $201.00  
  Purchase #2 $88.89   10.217%   $97.9719   $97.97   $97.95   $98.00  
  Purchase #3 $125.32   12.441%   $140.9111   $140.91   $140.90   $140.90  
  Purchase #4 $235.61   5.639%   $248.896   $248.90   $248.90   $248.90  
  Purchase #5 $88.73   10.606%   $98.1407   $98.14   $98.15   $98.10  
  Purchase #6 $47.27   3.167%   $48.767   $48.77   $48.75   $48.80  
  Purchase #7 $12.39   7.312%   $13.296   $13.30   $13.30   $13.30  
  7 purchase totals = $779.95       $848.9453   $848.95   $848.90   $849.00