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	$247.55	8.506%	$268.6066	$268.61	$268.60	$268.60
Purchase #2	$160.25	7.573%	$172.3857	$172.39	$172.40	$172.40
Purchase #3	$223.70	13.580%	$254.0785	$254.08	$254.10	$254.10
Purchase #4	$169.93	9.184%	$185.5364	$185.54	$185.55	$185.50
Purchase #5	$40.80	13.535%	$46.3223	$46.32	$46.30	$46.30
Purchase #6	$140.65	4.168%	$146.5123	$146.51	$146.50	$146.50
Purchase #7	$234.91	9.434%	$257.0714	$257.07	$257.05	$257.10
7 purchase totals =	$1,217.79		$1,330.5132	$1,330.52	$1,330.50	$1,330.50