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	$34.49	8.594%	$37.4541	$37.45	$37.45	$37.50
Purchase #2	$242.33	5.547%	$255.772	$255.77	$255.75	$255.80
Purchase #3	$48.88	10.245%	$53.8878	$53.89	$53.90	$53.90
Purchase #4	$132.89	10.444%	$146.769	$146.77	$146.75	$146.80
Purchase #5	$106.29	12.354%	$119.4211	$119.42	$119.40	$119.40
Purchase #6	$199.52	7.561%	$214.6057	$214.61	$214.60	$214.60
Purchase #7	$53.52	4.476%	$55.9156	$55.92	$55.90	$55.90
7 purchase totals =	$817.92		$883.8253	$883.83	$883.75	$883.90