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	$78.77	13.472%	$89.3819	$89.38	$89.40	$89.40
Purchase #2	$168.54	3.867%	$175.0574	$175.06	$175.05	$175.10
Purchase #3	$175.71	11.789%	$196.4245	$196.42	$196.40	$196.40
Purchase #4	$144.25	4.581%	$150.8581	$150.86	$150.85	$150.90
Purchase #5	$223.94	5.224%	$235.6386	$235.64	$235.65	$235.60
Purchase #6	$40.94	12.391%	$46.0129	$46.01	$46.00	$46.00
Purchase #7	$207.55	3.295%	$214.3888	$214.39	$214.40	$214.40
7 purchase totals =	$1,039.70		$1,107.7622	$1,107.76	$1,107.75	$1,107.80