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	$155.35	11.818%	$173.7093	$173.71	$173.70	$173.70
Purchase #2	$158.59	7.657%	$170.7332	$170.73	$170.75	$170.70
Purchase #3	$183.61	3.612%	$190.242	$190.24	$190.25	$190.20
Purchase #4	$30.45	9.358%	$33.2995	$33.30	$33.30	$33.30
Purchase #5	$73.52	6.284%	$78.14	$78.14	$78.15	$78.10
Purchase #6	$128.85	11.649%	$143.8597	$143.86	$143.85	$143.90
Purchase #7	$174.55	9.258%	$190.7098	$190.71	$190.70	$190.70
7 purchase totals =	$904.92		$980.6935	$980.69	$980.70	$980.60