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	$120.58	8.852%	$131.2537	$131.25	$131.25	$131.30
Purchase #2	$9.63	10.425%	$10.6339	$10.63	$10.65	$10.60
Purchase #3	$62.98	4.514%	$65.8229	$65.82	$65.80	$65.80
Purchase #4	$30.59	11.318%	$34.0522	$34.05	$34.05	$34.10
Purchase #5	$160.34	12.687%	$180.6823	$180.68	$180.70	$180.70
Purchase #6	$149.32	10.852%	$165.5242	$165.52	$165.50	$165.50
Purchase #7	$40.54	4.658%	$42.4284	$42.43	$42.45	$42.40
7 purchase totals =	$573.98		$630.3976	$630.38	$630.40	$630.40