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	$72.41	8.232%	$78.3708	$78.37	$78.35	$78.40
Purchase #2	$23.99	3.206%	$24.7591	$24.76	$24.75	$24.80
Purchase #3	$147.50	7.194%	$158.1112	$158.11	$158.10	$158.10
Purchase #4	$173.70	13.197%	$196.6232	$196.62	$196.60	$196.60
Purchase #5	$219.88	9.324%	$240.3816	$240.38	$240.40	$240.40
Purchase #6	$134.76	7.765%	$145.2241	$145.22	$145.20	$145.20
Purchase #7	$56.45	9.872%	$62.0227	$62.02	$62.00	$62.00
7 purchase totals =	$828.69		$905.4927	$905.48	$905.40	$905.50