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	$17.70	11.593%	$19.752	$19.75	$19.75	$19.80
Purchase #2	$132.25	9.846%	$145.2713	$145.27	$145.25	$145.30
Purchase #3	$139.68	4.804%	$146.3902	$146.39	$146.40	$146.40
Purchase #4	$104.78	6.633%	$111.7301	$111.73	$111.75	$111.70
Purchase #5	$76.94	10.699%	$85.1718	$85.17	$85.15	$85.20
Purchase #6	$149.63	10.636%	$165.5446	$165.54	$165.55	$165.50
Purchase #7	$221.27	12.864%	$249.7342	$249.73	$249.75	$249.70
7 purchase totals =	$842.25		$923.5942	$923.58	$923.60	$923.60