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	$69.88	12.389%	$78.5374	$78.54	$78.55	$78.50
Purchase #2	$46.33	10.206%	$51.0584	$51.06	$51.05	$51.10
Purchase #3	$128.72	13.603%	$146.2298	$146.23	$146.25	$146.20
Purchase #4	$17.62	5.600%	$18.6067	$18.61	$18.60	$18.60
Purchase #5	$77.64	3.551%	$80.397	$80.40	$80.40	$80.40
Purchase #6	$145.56	13.828%	$165.688	$165.69	$165.70	$165.70
Purchase #7	$204.40	5.826%	$216.3083	$216.31	$216.30	$216.30
7 purchase totals =	$690.15		$756.8256	$756.84	$756.85	$756.80