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 $69.44   10.171%   $76.5027   $76.50   $76.50   $76.50  
  Purchase #2 $112.47   11.821%   $125.7651   $125.77   $125.75   $125.80  
  Purchase #3 $168.98   4.727%   $176.9677   $176.97   $176.95   $177.00  
  Purchase #4 $200.88   6.509%   $213.9553   $213.96   $213.95   $214.00  
  Purchase #5 $148.79   5.723%   $157.3053   $157.31   $157.30   $157.30  
  Purchase #6 $94.29   4.371%   $98.4114   $98.41   $98.40   $98.40  
  Purchase #7 $41.44   13.629%   $47.0879   $47.09   $47.10   $47.10  
  7 purchase totals = $836.29       $895.9954   $896.01   $895.95   $896.10