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	$83.61	7.728%	$90.0714	$90.07	$90.05	$90.10
Purchase #2	$129.71	10.638%	$143.5085	$143.51	$143.50	$143.50
Purchase #3	$46.65	5.699%	$49.3086	$49.31	$49.30	$49.30
Purchase #4	$172.28	12.827%	$194.3784	$194.38	$194.40	$194.40
Purchase #5	$65.88	10.178%	$72.5853	$72.59	$72.60	$72.60
Purchase #6	$114.75	6.163%	$121.822	$121.82	$121.80	$121.80
Purchase #7	$208.60	13.367%	$236.4836	$236.48	$236.50	$236.50
7 purchase totals =	$821.48		$908.1578	$908.16	$908.15	$908.20