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	$86.75	4.484%	$90.6399	$90.64	$90.65	$90.60
Purchase #2	$29.99	3.433%	$31.0196	$31.02	$31.00	$31.00
Purchase #3	$21.40	10.195%	$23.5817	$23.58	$23.60	$23.60
Purchase #4	$33.82	4.192%	$35.2377	$35.24	$35.25	$35.20
Purchase #5	$135.61	13.170%	$153.4698	$153.47	$153.45	$153.50
Purchase #6	$217.91	13.570%	$247.4804	$247.48	$247.50	$247.50
Purchase #7	$120.99	5.240%	$127.3299	$127.33	$127.35	$127.30
7 purchase totals =	$646.47		$708.7590	$708.76	$708.80	$708.70