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	$145.43	8.844%	$158.2918	$158.29	$158.30	$158.30
Purchase #2	$179.63	3.423%	$185.7787	$185.78	$185.80	$185.80
Purchase #3	$244.36	4.380%	$255.063	$255.06	$255.05	$255.10
Purchase #4	$104.51	13.125%	$118.2269	$118.23	$118.25	$118.20
Purchase #5	$156.99	9.379%	$171.7141	$171.71	$171.70	$171.70
Purchase #6	$7.40	4.671%	$7.7457	$7.75	$7.75	$7.70
Purchase #7	$32.57	12.404%	$36.61	$36.61	$36.60	$36.60
7 purchase totals =	$870.89		$933.4302	$933.43	$933.45	$933.40