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 $41.63   11.697%   $46.4995   $46.50   $46.50   $46.50  
  Purchase #2 $202.43   10.783%   $224.258   $224.26   $224.25   $224.30  
  Purchase #3 $63.76   7.153%   $68.3208   $68.32   $68.30   $68.30  
  Purchase #4 $133.64   10.321%   $147.433   $147.43   $147.45   $147.40  
  Purchase #5 $163.33   3.805%   $169.5447   $169.54   $169.55   $169.50  
  Purchase #6 $101.72   8.741%   $110.6113   $110.61   $110.60   $110.60  
  Purchase #7 $27.63   10.130%   $30.4289   $30.43   $30.45   $30.40  
  7 purchase totals = $734.14       $797.0962   $797.09   $797.10   $797.00