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	$90.42	10.720%	$100.113	$100.11	$100.10	$100.10
Purchase #2	$85.91	3.289%	$88.7356	$88.74	$88.75	$88.70
Purchase #3	$50.25	8.853%	$54.6986	$54.70	$54.70	$54.70
Purchase #4	$10.91	11.669%	$12.1831	$12.18	$12.20	$12.20
Purchase #5	$34.77	5.524%	$36.6907	$36.69	$36.70	$36.70
Purchase #6	$236.90	4.215%	$246.8853	$246.89	$246.90	$246.90
Purchase #7	$96.92	3.494%	$100.3064	$100.31	$100.30	$100.30
7 purchase totals =	$606.08		$639.6127	$639.62	$639.65	$639.60