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	$238.26	8.271%	$257.9665	$257.97	$257.95	$258.00
Purchase #2	$143.85	4.587%	$150.4484	$150.45	$150.45	$150.40
Purchase #3	$36.37	11.680%	$40.618	$40.62	$40.60	$40.60
Purchase #4	$144.72	10.143%	$159.3989	$159.40	$159.40	$159.40
Purchase #5	$232.39	9.689%	$254.9063	$254.91	$254.90	$254.90
Purchase #6	$153.36	8.170%	$165.8895	$165.89	$165.90	$165.90
Purchase #7	$187.70	3.487%	$194.2451	$194.25	$194.25	$194.20
7 purchase totals =	$1,136.65		$1,223.4727	$1,223.49	$1,223.45	$1,223.40