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	$156.85	10.512%	$173.3381	$173.34	$173.35	$173.30
Purchase #2	$60.33	12.186%	$67.6818	$67.68	$67.70	$67.70
Purchase #3	$173.95	6.467%	$185.1993	$185.20	$185.20	$185.20
Purchase #4	$119.79	10.789%	$132.7141	$132.71	$132.70	$132.70
Purchase #5	$200.69	3.862%	$208.4406	$208.44	$208.45	$208.40
Purchase #6	$63.46	13.607%	$72.095	$72.10	$72.10	$72.10
Purchase #7	$144.55	4.514%	$151.075	$151.08	$151.10	$151.10
7 purchase totals =	$919.62		$990.5439	$990.55	$990.60	$990.50