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	$129.69	10.853%	$143.7653	$143.77	$143.75	$143.80
Purchase #2	$192.81	3.231%	$199.0397	$199.04	$199.05	$199.00
Purchase #3	$103.87	4.535%	$108.5805	$108.58	$108.60	$108.60
Purchase #4	$105.31	5.831%	$111.4506	$111.45	$111.45	$111.50
Purchase #5	$90.96	11.422%	$101.3495	$101.35	$101.35	$101.30
Purchase #6	$79.83	10.596%	$88.2888	$88.29	$88.30	$88.30
Purchase #7	$235.74	4.580%	$246.5369	$246.54	$246.55	$246.50
7 purchase totals =	$938.21		$999.0113	$999.02	$999.05	$999.00