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	$30.30	3.823%	$31.4584	$31.46	$31.45	$31.50
Purchase #2	$98.31	5.366%	$103.5853	$103.59	$103.60	$103.60
Purchase #3	$134.71	3.638%	$139.6107	$139.61	$139.60	$139.60
Purchase #4	$119.94	12.246%	$134.6279	$134.63	$134.65	$134.60
Purchase #5	$30.52	9.501%	$33.4197	$33.42	$33.40	$33.40
Purchase #6	$164.27	11.505%	$183.1693	$183.17	$183.15	$183.20
Purchase #7	$154.62	13.860%	$176.0503	$176.05	$176.05	$176.10
7 purchase totals =	$732.67		$801.9216	$801.93	$801.90	$802.00