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	$134.31	3.588%	$139.129	$139.13	$139.15	$139.10
Purchase #2	$115.78	13.599%	$131.5249	$131.52	$131.50	$131.50
Purchase #3	$60.83	4.314%	$63.4542	$63.45	$63.45	$63.50
Purchase #4	$91.81	9.633%	$100.6541	$100.65	$100.65	$100.70
Purchase #5	$199.46	11.178%	$221.7556	$221.76	$221.75	$221.80
Purchase #6	$152.33	4.852%	$159.7211	$159.72	$159.70	$159.70
Purchase #7	$85.93	13.123%	$97.2066	$97.21	$97.20	$97.20
7 purchase totals =	$840.45		$913.4455	$913.44	$913.40	$913.50