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	$18.79	9.841%	$20.6391	$20.64	$20.65	$20.60
Purchase #2	$200.44	5.500%	$211.4642	$211.46	$211.45	$211.50
Purchase #3	$96.54	3.774%	$100.1834	$100.18	$100.20	$100.20
Purchase #4	$117.69	7.810%	$126.8816	$126.88	$126.90	$126.90
Purchase #5	$78.85	3.103%	$81.2967	$81.30	$81.30	$81.30
Purchase #6	$226.54	6.588%	$241.4645	$241.46	$241.45	$241.50
Purchase #7	$177.67	12.430%	$199.7544	$199.75	$199.75	$199.80
7 purchase totals =	$916.52		$981.6839	$981.67	$981.70	$981.80