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	$171.71	4.149%	$178.8342	$178.83	$178.85	$178.80
Purchase #2	$190.43	11.691%	$212.6932	$212.69	$212.70	$212.70
Purchase #3	$6.87	9.305%	$7.5093	$7.51	$7.50	$7.50
Purchase #4	$134.90	3.379%	$139.4583	$139.46	$139.45	$139.50
Purchase #5	$48.82	8.856%	$53.1435	$53.14	$53.15	$53.10
Purchase #6	$72.30	8.329%	$78.3219	$78.32	$78.30	$78.30
Purchase #7	$165.63	4.677%	$173.3765	$173.38	$173.40	$173.40
7 purchase totals =	$790.66		$843.3369	$843.33	$843.35	$843.30