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	$72.32	6.859%	$77.2804	$77.28	$77.30	$77.30
Purchase #2	$54.25	4.350%	$56.6099	$56.61	$56.60	$56.60
Purchase #3	$72.60	8.162%	$78.5256	$78.53	$78.55	$78.50
Purchase #4	$224.88	11.528%	$250.8042	$250.80	$250.80	$250.80
Purchase #5	$26.82	4.641%	$28.0647	$28.06	$28.05	$28.10
Purchase #6	$12.43	5.222%	$13.0791	$13.08	$13.10	$13.10
Purchase #7	$16.30	10.504%	$18.0122	$18.01	$18.00	$18.00
7 purchase totals =	$479.60		$522.3761	$522.37	$522.40	$522.40