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	$149.34	5.857%	$158.0868	$158.09	$158.10	$158.10
Purchase #2	$134.70	8.127%	$145.6471	$145.65	$145.65	$145.60
Purchase #3	$220.97	6.162%	$234.5862	$234.59	$234.60	$234.60
Purchase #4	$56.84	4.102%	$59.1716	$59.17	$59.15	$59.20
Purchase #5	$127.53	11.395%	$142.062	$142.06	$142.05	$142.10
Purchase #6	$88.38	13.415%	$100.2362	$100.24	$100.25	$100.20
Purchase #7	$104.92	5.335%	$110.5175	$110.52	$110.50	$110.50
7 purchase totals =	$882.68		$950.3074	$950.32	$950.30	$950.30