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	$10.77	9.465%	$11.7894	$11.79	$11.80	$11.80
Purchase #2	$17.60	5.766%	$18.6148	$18.61	$18.60	$18.60
Purchase #3	$191.57	10.549%	$211.7787	$211.78	$211.80	$211.80
Purchase #4	$42.91	5.277%	$45.1744	$45.17	$45.15	$45.20
Purchase #5	$97.33	10.786%	$107.828	$107.83	$107.85	$107.80
Purchase #6	$220.57	9.454%	$241.4227	$241.42	$241.40	$241.40
Purchase #7	$137.64	6.287%	$146.2934	$146.29	$146.30	$146.30
7 purchase totals =	$718.39		$782.9014	$782.89	$782.90	$782.90