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	$28.67	5.512%	$30.2503	$30.25	$30.25	$30.30
Purchase #2	$91.67	9.262%	$100.1605	$100.16	$100.15	$100.20
Purchase #3	$126.82	13.488%	$143.9255	$143.93	$143.95	$143.90
Purchase #4	$134.86	11.638%	$150.555	$150.56	$150.55	$150.60
Purchase #5	$40.48	11.437%	$45.1097	$45.11	$45.10	$45.10
Purchase #6	$134.93	6.255%	$143.3699	$143.37	$143.35	$143.40
Purchase #7	$246.69	11.779%	$275.7476	$275.75	$275.75	$275.70
7 purchase totals =	$804.12		$889.1185	$889.13	$889.10	$889.20