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	$49.90	5.242%	$52.5158	$52.52	$52.50	$52.50
Purchase #2	$144.71	9.114%	$157.8989	$157.90	$157.90	$157.90
Purchase #3	$77.72	4.139%	$80.9368	$80.94	$80.95	$80.90
Purchase #4	$188.36	3.195%	$194.3781	$194.38	$194.40	$194.40
Purchase #5	$29.41	12.411%	$33.0601	$33.06	$33.05	$33.10
Purchase #6	$214.99	13.595%	$244.2179	$244.22	$244.20	$244.20
Purchase #7	$191.50	4.152%	$199.4511	$199.45	$199.45	$199.50
7 purchase totals =	$896.59		$962.4587	$962.47	$962.45	$962.50