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	$76.35	5.372%	$80.4515	$80.45	$80.45	$80.50
Purchase #2	$116.59	7.222%	$125.0101	$125.01	$125.00	$125.00
Purchase #3	$106.74	4.230%	$111.2551	$111.26	$111.25	$111.30
Purchase #4	$106.51	10.235%	$117.4113	$117.41	$117.40	$117.40
Purchase #5	$129.38	11.131%	$143.7813	$143.78	$143.80	$143.80
Purchase #6	$17.27	11.831%	$19.3132	$19.31	$19.30	$19.30
Purchase #7	$40.67	11.644%	$45.4056	$45.41	$45.40	$45.40
7 purchase totals =	$593.51		$642.6281	$642.63	$642.60	$642.70