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	$35.27	13.279%	$39.9535	$39.95	$39.95	$40.00
Purchase #2	$27.60	3.324%	$28.5174	$28.52	$28.50	$28.50
Purchase #3	$244.98	12.498%	$275.5976	$275.60	$275.60	$275.60
Purchase #4	$99.33	12.663%	$111.9082	$111.91	$111.90	$111.90
Purchase #5	$129.67	12.405%	$145.7556	$145.76	$145.75	$145.80
Purchase #6	$231.33	10.690%	$256.0592	$256.06	$256.05	$256.10
Purchase #7	$233.45	3.633%	$241.9312	$241.93	$241.95	$241.90
7 purchase totals =	$1,001.63		$1,099.7227	$1,099.73	$1,099.70	$1,099.80