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	$46.55	8.514%	$50.5133	$50.51	$50.50	$50.50
Purchase #2	$149.84	8.364%	$162.3726	$162.37	$162.35	$162.40
Purchase #3	$250.30	10.108%	$275.6003	$275.60	$275.60	$275.60
Purchase #4	$40.72	12.717%	$45.8984	$45.90	$45.90	$45.90
Purchase #5	$174.62	7.180%	$187.1577	$187.16	$187.15	$187.20
Purchase #6	$23.68	8.405%	$25.6703	$25.67	$25.65	$25.70
Purchase #7	$88.60	9.325%	$96.862	$96.86	$96.85	$96.90
7 purchase totals =	$774.31		$844.0746	$844.07	$844.00	$844.20