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	$155.42	13.379%	$176.2136	$176.21	$176.20	$176.20
Purchase #2	$47.29	11.748%	$52.8456	$52.85	$52.85	$52.80
Purchase #3	$40.78	9.366%	$44.5995	$44.60	$44.60	$44.60
Purchase #4	$181.65	10.180%	$200.142	$200.14	$200.15	$200.10
Purchase #5	$31.75	4.774%	$33.2657	$33.27	$33.25	$33.30
Purchase #6	$74.61	10.142%	$82.1769	$82.18	$82.20	$82.20
Purchase #7	$215.85	11.675%	$241.0505	$241.05	$241.05	$241.10
7 purchase totals =	$747.35		$830.2938	$830.30	$830.30	$830.30