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	$49.59	11.335%	$55.211	$55.21	$55.20	$55.20
Purchase #2	$19.30	9.471%	$21.1279	$21.13	$21.15	$21.10
Purchase #3	$181.98	4.859%	$190.8224	$190.82	$190.80	$190.80
Purchase #4	$155.34	11.674%	$173.4744	$173.47	$173.45	$173.50
Purchase #5	$41.37	13.606%	$46.9988	$47.00	$47.00	$47.00
Purchase #6	$127.90	13.428%	$145.0744	$145.07	$145.05	$145.10
Purchase #7	$162.35	12.354%	$182.4067	$182.41	$182.40	$182.40
7 purchase totals =	$737.83		$815.1156	$815.11	$815.05	$815.10