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	$8.29	6.688%	$8.8444	$8.84	$8.85	$8.80
Purchase #2	$47.64	11.639%	$53.1848	$53.18	$53.20	$53.20
Purchase #3	$20.61	7.102%	$22.0737	$22.07	$22.05	$22.10
Purchase #4	$30.46	3.196%	$31.4335	$31.43	$31.45	$31.40
Purchase #5	$8.32	3.267%	$8.5918	$8.59	$8.60	$8.60
Purchase #6	$53.49	12.103%	$59.9639	$59.96	$59.95	$60.00
Purchase #7	$108.66	5.393%	$114.52	$114.52	$114.50	$114.50
7 purchase totals =	$277.47		$298.6121	$298.59	$298.60	$298.60