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	$201.69	12.802%	$227.5104	$227.51	$227.50	$227.50
Purchase #2	$42.47	13.296%	$48.1168	$48.12	$48.10	$48.10
Purchase #3	$47.50	10.437%	$52.4576	$52.46	$52.45	$52.50
Purchase #4	$157.75	7.535%	$169.6365	$169.64	$169.65	$169.60
Purchase #5	$81.47	10.699%	$90.1865	$90.19	$90.20	$90.20
Purchase #6	$100.58	6.801%	$107.4204	$107.42	$107.40	$107.40
Purchase #7	$140.67	12.327%	$158.0104	$158.01	$158.00	$158.00
7 purchase totals =	$772.13		$853.3386	$853.35	$853.30	$853.30