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	$91.42	13.716%	$103.9592	$103.96	$103.95	$104.00
Purchase #2	$131.82	4.632%	$137.9259	$137.93	$137.95	$137.90
Purchase #3	$35.31	8.445%	$38.2919	$38.29	$38.30	$38.30
Purchase #4	$113.62	12.764%	$128.1225	$128.12	$128.10	$128.10
Purchase #5	$94.95	6.338%	$100.9679	$100.97	$100.95	$101.00
Purchase #6	$11.82	9.380%	$12.9287	$12.93	$12.95	$12.90
Purchase #7	$38.57	12.612%	$43.4344	$43.43	$43.45	$43.40
7 purchase totals =	$517.51		$565.6305	$565.63	$565.65	$565.60