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	$11.90	3.256%	$12.2875	$12.29	$12.30	$12.30
Purchase #2	$125.92	4.711%	$131.8521	$131.85	$131.85	$131.90
Purchase #3	$213.91	7.851%	$230.7041	$230.70	$230.70	$230.70
Purchase #4	$52.32	7.275%	$56.1263	$56.13	$56.15	$56.10
Purchase #5	$127.27	3.805%	$132.1126	$132.11	$132.10	$132.10
Purchase #6	$50.38	7.323%	$54.0693	$54.07	$54.05	$54.10
Purchase #7	$183.73	11.739%	$205.2981	$205.30	$205.30	$205.30
7 purchase totals =	$765.43		$822.4500	$822.45	$822.45	$822.50