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	$234.44	4.857%	$245.8268	$245.83	$245.85	$245.80
Purchase #2	$62.27	11.348%	$69.3364	$69.34	$69.35	$69.30
Purchase #3	$51.62	3.240%	$53.2925	$53.29	$53.30	$53.30
Purchase #4	$189.65	5.680%	$200.4221	$200.42	$200.40	$200.40
Purchase #5	$111.33	6.404%	$118.4596	$118.46	$118.45	$118.50
Purchase #6	$27.38	10.406%	$30.2292	$30.23	$30.25	$30.20
Purchase #7	$103.47	8.713%	$112.4853	$112.49	$112.50	$112.50
7 purchase totals =	$780.16		$830.0519	$830.06	$830.10	$830.00