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	$18.66	5.737%	$19.7305	$19.73	$19.75	$19.70
Purchase #2	$106.60	7.765%	$114.8775	$114.88	$114.90	$114.90
Purchase #3	$53.84	10.143%	$59.301	$59.30	$59.30	$59.30
Purchase #4	$156.49	10.791%	$173.3768	$173.38	$173.40	$173.40
Purchase #5	$132.42	13.329%	$150.0703	$150.07	$150.05	$150.10
Purchase #6	$30.83	3.111%	$31.7891	$31.79	$31.80	$31.80
Purchase #7	$37.95	5.871%	$40.178	$40.18	$40.20	$40.20
7 purchase totals =	$536.79		$589.3232	$589.33	$589.40	$589.40