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	$243.50	6.537%	$259.4176	$259.42	$259.40	$259.40
Purchase #2	$175.87	4.576%	$183.9178	$183.92	$183.90	$183.90
Purchase #3	$124.50	5.425%	$131.2541	$131.25	$131.25	$131.30
Purchase #4	$171.54	4.551%	$179.3468	$179.35	$179.35	$179.30
Purchase #5	$144.68	10.491%	$159.8584	$159.86	$159.85	$159.90
Purchase #6	$74.56	12.434%	$83.8308	$83.83	$83.85	$83.80
Purchase #7	$22.46	9.829%	$24.6676	$24.67	$24.65	$24.70
7 purchase totals =	$957.11		$1,022.2931	$1,022.30	$1,022.25	$1,022.30