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	$155.45	11.844%	$173.8615	$173.86	$173.85	$173.90
Purchase #2	$19.65	4.326%	$20.5001	$20.50	$20.50	$20.50
Purchase #3	$128.25	6.179%	$136.1746	$136.17	$136.15	$136.20
Purchase #4	$106.62	4.827%	$111.7665	$111.77	$111.75	$111.80
Purchase #5	$53.86	12.645%	$60.6706	$60.67	$60.65	$60.70
Purchase #6	$45.41	13.657%	$51.6116	$51.61	$51.60	$51.60
Purchase #7	$122.58	9.611%	$134.3612	$134.36	$134.35	$134.40
7 purchase totals =	$631.82		$688.9461	$688.94	$688.85	$689.10