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	$7.86	5.679%	$8.3064	$8.31	$8.30	$8.30
Purchase #2	$152.89	7.456%	$164.2895	$164.29	$164.30	$164.30
Purchase #3	$213.61	13.149%	$241.6976	$241.70	$241.70	$241.70
Purchase #4	$171.76	12.403%	$193.0634	$193.06	$193.05	$193.10
Purchase #5	$158.92	13.131%	$179.7878	$179.79	$179.80	$179.80
Purchase #6	$102.45	3.347%	$105.879	$105.88	$105.90	$105.90
Purchase #7	$115.56	9.679%	$126.7451	$126.75	$126.75	$126.70
7 purchase totals =	$923.05		$1,019.7688	$1,019.78	$1,019.80	$1,019.80