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	$105.83	12.141%	$118.6788	$118.68	$118.70	$118.70
Purchase #2	$34.31	10.450%	$37.8954	$37.90	$37.90	$37.90
Purchase #3	$146.75	7.520%	$157.7856	$157.79	$157.80	$157.80
Purchase #4	$53.72	6.823%	$57.3853	$57.39	$57.40	$57.40
Purchase #5	$62.41	10.618%	$69.0367	$69.04	$69.05	$69.00
Purchase #6	$100.64	4.790%	$105.4607	$105.46	$105.45	$105.50
Purchase #7	$171.88	6.808%	$183.5816	$183.58	$183.60	$183.60
7 purchase totals =	$675.54		$729.8241	$729.84	$729.90	$729.90