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	$93.82	6.771%	$100.1726	$100.17	$100.15	$100.20
Purchase #2	$133.80	12.707%	$150.802	$150.80	$150.80	$150.80
Purchase #3	$90.37	13.325%	$102.4118	$102.41	$102.40	$102.40
Purchase #4	$105.29	3.206%	$108.6656	$108.67	$108.65	$108.70
Purchase #5	$211.56	4.187%	$220.418	$220.42	$220.40	$220.40
Purchase #6	$100.40	3.861%	$104.2764	$104.28	$104.30	$104.30
Purchase #7	$177.77	7.868%	$191.7569	$191.76	$191.75	$191.80
7 purchase totals =	$913.01		$978.5033	$978.51	$978.45	$978.60