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	$12.42	10.614%	$13.7383	$13.74	$13.75	$13.70
Purchase #2	$112.43	11.721%	$125.6079	$125.61	$125.60	$125.60
Purchase #3	$54.64	9.225%	$59.6805	$59.68	$59.70	$59.70
Purchase #4	$158.82	4.835%	$166.4989	$166.50	$166.50	$166.50
Purchase #5	$167.30	13.714%	$190.2435	$190.24	$190.25	$190.20
Purchase #6	$132.98	13.612%	$151.0812	$151.08	$151.10	$151.10
Purchase #7	$179.30	7.749%	$193.194	$193.19	$193.20	$193.20
7 purchase totals =	$817.89		$900.0443	$900.04	$900.10	$900.00