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	$139.70	11.274%	$155.4498	$155.45	$155.45	$155.40
Purchase #2	$204.65	9.404%	$223.8953	$223.90	$223.90	$223.90
Purchase #3	$53.35	4.755%	$55.8868	$55.89	$55.90	$55.90
Purchase #4	$50.78	11.659%	$56.7004	$56.70	$56.70	$56.70
Purchase #5	$47.88	13.608%	$54.3955	$54.40	$54.40	$54.40
Purchase #6	$235.97	10.307%	$260.2914	$260.29	$260.30	$260.30
Purchase #7	$176.63	3.381%	$182.6019	$182.60	$182.60	$182.60
7 purchase totals =	$908.96		$989.2211	$989.23	$989.25	$989.20