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	$146.42	11.578%	$163.3725	$163.37	$163.35	$163.40
Purchase #2	$76.97	8.171%	$83.2592	$83.26	$83.25	$83.30
Purchase #3	$108.52	4.820%	$113.7507	$113.75	$113.75	$113.80
Purchase #4	$228.25	3.373%	$235.9489	$235.95	$235.95	$235.90
Purchase #5	$86.65	4.613%	$90.6472	$90.65	$90.65	$90.60
Purchase #6	$80.29	11.781%	$89.749	$89.75	$89.75	$89.70
Purchase #7	$115.69	13.762%	$131.6113	$131.61	$131.60	$131.60
7 purchase totals =	$842.79		$908.3388	$908.34	$908.30	$908.30