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	$145.53	9.541%	$159.415	$159.42	$159.40	$159.40
Purchase #2	$137.77	13.759%	$156.7258	$156.73	$156.75	$156.70
Purchase #3	$214.70	12.466%	$241.4645	$241.46	$241.45	$241.50
Purchase #4	$129.70	3.591%	$134.3575	$134.36	$134.35	$134.40
Purchase #5	$25.54	7.838%	$27.5418	$27.54	$27.55	$27.50
Purchase #6	$191.60	4.857%	$200.906	$200.91	$200.90	$200.90
Purchase #7	$88.88	13.268%	$100.6726	$100.67	$100.65	$100.70
7 purchase totals =	$933.72		$1,021.0832	$1,021.09	$1,021.05	$1,021.10