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	$115.52	8.296%	$125.1035	$125.10	$125.10	$125.10
Purchase #2	$155.85	10.805%	$172.6896	$172.69	$172.70	$172.70
Purchase #3	$52.65	13.169%	$59.5835	$59.58	$59.60	$59.60
Purchase #4	$73.31	13.662%	$83.3256	$83.33	$83.35	$83.30
Purchase #5	$101.91	5.421%	$107.4345	$107.43	$107.45	$107.40
Purchase #6	$156.27	4.252%	$162.9146	$162.91	$162.90	$162.90
Purchase #7	$83.29	5.694%	$88.0325	$88.03	$88.05	$88.00
7 purchase totals =	$738.80		$799.0838	$799.07	$799.15	$799.00