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	$80.91	10.203%	$89.1652	$89.17	$89.15	$89.20
Purchase #2	$14.61	5.776%	$15.4539	$15.45	$15.45	$15.50
Purchase #3	$113.77	5.758%	$120.3209	$120.32	$120.30	$120.30
Purchase #4	$65.60	12.873%	$74.0447	$74.04	$74.05	$74.00
Purchase #5	$164.58	4.493%	$171.9746	$171.97	$171.95	$172.00
Purchase #6	$78.74	4.155%	$82.0116	$82.01	$82.00	$82.00
Purchase #7	$27.33	9.294%	$29.8701	$29.87	$29.85	$29.90
7 purchase totals =	$545.54		$582.8410	$582.83	$582.75	$582.90