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	$30.63	11.816%	$34.2492	$34.25	$34.25	$34.20
Purchase #2	$85.83	4.343%	$89.5576	$89.56	$89.55	$89.60
Purchase #3	$12.92	12.317%	$14.5114	$14.51	$14.50	$14.50
Purchase #4	$112.84	13.208%	$127.7439	$127.74	$127.75	$127.70
Purchase #5	$57.83	13.393%	$65.5752	$65.58	$65.60	$65.60
Purchase #6	$140.27	8.531%	$152.2364	$152.24	$152.25	$152.20
Purchase #7	$155.63	3.530%	$161.1237	$161.12	$161.10	$161.10
7 purchase totals =	$595.95		$644.9974	$645.00	$645.00	$644.90