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	$15.68	8.471%	$17.0083	$17.01	$17.00	$17.00
Purchase #2	$71.54	9.770%	$78.5295	$78.53	$78.55	$78.50
Purchase #3	$171.81	8.239%	$185.9654	$185.97	$185.95	$186.00
Purchase #4	$80.78	13.105%	$91.3662	$91.37	$91.35	$91.40
Purchase #5	$5.78	6.301%	$6.1442	$6.14	$6.15	$6.10
Purchase #6	$48.69	12.632%	$54.8405	$54.84	$54.85	$54.80
Purchase #7	$141.27	3.670%	$146.4546	$146.45	$146.45	$146.50
7 purchase totals =	$535.55		$580.3087	$580.31	$580.30	$580.30