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	$202.50	10.367%	$223.4932	$223.49	$223.50	$223.50
Purchase #2	$107.31	12.622%	$120.8547	$120.85	$120.85	$120.90
Purchase #3	$131.70	11.104%	$146.324	$146.32	$146.30	$146.30
Purchase #4	$241.30	9.505%	$264.2356	$264.24	$264.25	$264.20
Purchase #5	$17.64	4.403%	$18.4167	$18.42	$18.40	$18.40
Purchase #6	$130.30	12.707%	$146.8572	$146.86	$146.85	$146.90
Purchase #7	$250.28	6.866%	$267.4642	$267.46	$267.45	$267.50
7 purchase totals =	$1,081.03		$1,187.6456	$1,187.64	$1,187.60	$1,187.70