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	$17.89	5.367%	$18.8502	$18.85	$18.85	$18.90
Purchase #2	$207.84	8.658%	$225.8348	$225.83	$225.85	$225.80
Purchase #3	$244.59	6.551%	$260.6131	$260.61	$260.60	$260.60
Purchase #4	$172.95	10.677%	$191.4159	$191.42	$191.40	$191.40
Purchase #5	$244.27	5.338%	$257.3091	$257.31	$257.30	$257.30
Purchase #6	$110.30	4.137%	$114.8631	$114.86	$114.85	$114.90
Purchase #7	$50.79	9.123%	$55.4236	$55.42	$55.40	$55.40
7 purchase totals =	$1,048.63		$1,124.3098	$1,124.30	$1,124.25	$1,124.30