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 $184.77   9.316%   $201.9832   $201.98   $202.00   $202.00  
  Purchase #2 $114.56   7.678%   $123.3559   $123.36   $123.35   $123.40  
  Purchase #3 $190.43   12.725%   $214.6622   $214.66   $214.65   $214.70  
  Purchase #4 $99.58   6.859%   $106.4102   $106.41   $106.40   $106.40  
  Purchase #5 $116.76   5.264%   $122.9062   $122.91   $122.90   $122.90  
  Purchase #6 $68.61   9.710%   $75.272   $75.27   $75.25   $75.30  
  Purchase #7 $115.80   4.566%   $121.0874   $121.09   $121.10   $121.10  
  7 purchase totals = $890.51       $965.6771   $965.68   $965.65   $965.80